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 $61.71   3.111%   $63.6298   $63.63   $63.65   $63.60  
  Purchase #2 $201.73   3.693%   $209.1799   $209.18   $209.20   $209.20  
  Purchase #3 $203.75   5.848%   $215.6653   $215.67   $215.65   $215.70  
  Purchase #4 $68.78   8.770%   $74.812   $74.81   $74.80   $74.80  
  Purchase #5 $160.56   5.317%   $169.097   $169.10   $169.10   $169.10  
  Purchase #6 $91.42   12.473%   $102.8228   $102.82   $102.80   $102.80  
  Purchase #7 $67.66   10.505%   $74.7677   $74.77   $74.75   $74.80  
  7 purchase totals = $855.61       $909.9745   $909.98   $909.95   $910.00