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 $244.45   9.689%   $268.1348   $268.13   $268.15   $268.10  
  Purchase #2 $220.86   7.181%   $236.72   $236.72   $236.70   $236.70  
  Purchase #3 $24.60   3.806%   $25.5363   $25.54   $25.55   $25.50  
  Purchase #4 $44.77   4.814%   $46.9252   $46.93   $46.95   $46.90  
  Purchase #5 $173.41   8.352%   $187.8932   $187.89   $187.90   $187.90  
  Purchase #6 $58.93   12.866%   $66.5119   $66.51   $66.50   $66.50  
  Purchase #7 $241.33   8.445%   $261.7103   $261.71   $261.70   $261.70  
  7 purchase totals = $1,008.35       $1,093.4317   $1,093.43   $1,093.45   $1,093.30