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 $57.97   8.227%   $62.7392   $62.74   $62.75   $62.70  
  Purchase #2 $46.84   9.218%   $51.1577   $51.16   $51.15   $51.20  
  Purchase #3 $125.88   5.132%   $132.3402   $132.34   $132.35   $132.30  
  Purchase #4 $201.78   9.492%   $220.933   $220.93   $220.95   $220.90  
  Purchase #5 $132.81   13.730%   $151.0448   $151.04   $151.05   $151.00  
  Purchase #6 $140.86   7.369%   $151.24   $151.24   $151.25   $151.20  
  Purchase #7 $17.74   11.236%   $19.7333   $19.73   $19.75   $19.70  
  7 purchase totals = $723.88       $789.1882   $789.18   $789.25   $789.00