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 $173.44   8.265%   $187.7748   $187.77   $187.75   $187.80  
  Purchase #2 $234.42   10.608%   $259.2873   $259.29   $259.30   $259.30  
  Purchase #3 $107.99   4.756%   $113.126   $113.13   $113.15   $113.10  
  Purchase #4 $86.92   12.272%   $97.5868   $97.59   $97.60   $97.60  
  Purchase #5 $125.41   10.289%   $138.3134   $138.31   $138.30   $138.30  
  Purchase #6 $27.86   4.829%   $29.2054   $29.21   $29.20   $29.20  
  Purchase #7 $116.39   6.542%   $124.0042   $124.00   $124.00   $124.00  
  7 purchase totals = $872.43       $949.2979   $949.30   $949.30   $949.30