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 $82.27   12.352%   $92.432   $92.43   $92.45   $92.40  
  Purchase #2 $121.42   3.495%   $125.6636   $125.66   $125.65   $125.70  
  Purchase #3 $120.96   13.328%   $137.0815   $137.08   $137.10   $137.10  
  Purchase #4 $194.69   7.524%   $209.3385   $209.34   $209.35   $209.30  
  Purchase #5 $101.65   10.856%   $112.6851   $112.69   $112.70   $112.70  
  Purchase #6 $112.96   11.355%   $125.7866   $125.79   $125.80   $125.80  
  Purchase #7 $19.86   5.536%   $20.9594   $20.96   $20.95   $21.00  
  7 purchase totals = $753.81       $823.9467   $823.95   $824.00   $824.00