Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $196.51   5.435%   $207.1903   $207.19   $207.20   $207.20  
  Purchase #2 $226.88   11.749%   $253.5361   $253.54   $253.55   $253.50  
  Purchase #3 $104.35   10.632%   $115.4445   $115.44   $115.45   $115.40  
  Purchase #4 $134.58   11.413%   $149.9396   $149.94   $149.95   $149.90  
  Purchase #5 $141.59   12.839%   $159.7687   $159.77   $159.75   $159.80  
  Purchase #6 $148.66   4.521%   $155.3809   $155.38   $155.40   $155.40  
  Purchase #7 $172.60   5.812%   $182.6315   $182.63   $182.65   $182.60  
  7 purchase totals = $1,125.17       $1,223.8916   $1,223.89   $1,223.95   $1,223.80