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 $88.78   11.217%   $98.7385   $98.74   $98.75   $98.70  
  Purchase #2 $92.77   4.760%   $97.1859   $97.19   $97.20   $97.20  
  Purchase #3 $15.31   8.149%   $16.5576   $16.56   $16.55   $16.60  
  Purchase #4 $139.62   9.361%   $152.6898   $152.69   $152.70   $152.70  
  Purchase #5 $132.31   13.126%   $149.677   $149.68   $149.70   $149.70  
  Purchase #6 $37.47   12.267%   $42.0664   $42.07   $42.05   $42.10  
  Purchase #7 $204.25   6.392%   $217.3057   $217.31   $217.30   $217.30  
  7 purchase totals = $710.51       $774.2209   $774.24   $774.25   $774.30