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 $38.52   13.203%   $43.6058   $43.61   $43.60   $43.60  
  Purchase #2 $177.49   8.718%   $192.9636   $192.96   $192.95   $193.00  
  Purchase #3 $198.57   5.344%   $209.1816   $209.18   $209.20   $209.20  
  Purchase #4 $23.69   11.842%   $26.4954   $26.50   $26.50   $26.50  
  Purchase #5 $212.60   7.236%   $227.9837   $227.98   $228.00   $228.00  
  Purchase #6 $82.69   5.252%   $87.0329   $87.03   $87.05   $87.00  
  Purchase #7 $113.46   8.740%   $123.3764   $123.38   $123.40   $123.40  
  7 purchase totals = $847.02       $910.6394   $910.64   $910.70   $910.70