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 $182.81   10.114%   $201.2994   $201.30   $201.30   $201.30  
  Purchase #2 $133.28   11.756%   $148.9484   $148.95   $148.95   $148.90  
  Purchase #3 $125.73   5.684%   $132.8765   $132.88   $132.90   $132.90  
  Purchase #4 $110.56   8.494%   $119.951   $119.95   $119.95   $120.00  
  Purchase #5 $69.87   6.327%   $74.2907   $74.29   $74.30   $74.30  
  Purchase #6 $194.67   4.427%   $203.288   $203.29   $203.30   $203.30  
  Purchase #7 $12.71   10.537%   $14.0493   $14.05   $14.05   $14.00  
  7 purchase totals = $829.63       $894.7033   $894.71   $894.75   $894.70