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 $88.59   6.591%   $94.429   $94.43   $94.45   $94.40  
  Purchase #2 $117.89   9.457%   $129.0389   $129.04   $129.05   $129.00  
  Purchase #3 $56.44   11.331%   $62.8352   $62.84   $62.85   $62.80  
  Purchase #4 $87.73   11.171%   $97.5303   $97.53   $97.55   $97.50  
  Purchase #5 $46.91   4.208%   $48.884   $48.88   $48.90   $48.90  
  Purchase #6 $248.26   5.594%   $262.1477   $262.15   $262.15   $262.10  
  Purchase #7 $245.63   13.855%   $279.662   $279.66   $279.65   $279.70  
  7 purchase totals = $891.45       $974.5271   $974.53   $974.60   $974.40