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 $55.53   13.799%   $63.1926   $63.19   $63.20   $63.20  
  Purchase #2 $168.33   8.514%   $182.6616   $182.66   $182.65   $182.70  
  Purchase #3 $123.49   5.585%   $130.3869   $130.39   $130.40   $130.40  
  Purchase #4 $117.50   10.269%   $129.5661   $129.57   $129.55   $129.60  
  Purchase #5 $108.31   4.364%   $113.0366   $113.04   $113.05   $113.00  
  Purchase #6 $117.29   11.705%   $131.0188   $131.02   $131.00   $131.00  
  Purchase #7 $51.95   12.766%   $58.5819   $58.58   $58.60   $58.60  
  7 purchase totals = $742.40       $808.4445   $808.45   $808.45   $808.50