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 $125.69   13.422%   $142.5601   $142.56   $142.55   $142.60  
  Purchase #2 $8.46   11.324%   $9.418   $9.42   $9.40   $9.40  
  Purchase #3 $62.82   9.118%   $68.5479   $68.55   $68.55   $68.50  
  Purchase #4 $194.38   9.352%   $212.5584   $212.56   $212.55   $212.60  
  Purchase #5 $58.28   6.779%   $62.2308   $62.23   $62.25   $62.20  
  Purchase #6 $184.31   9.249%   $201.3568   $201.36   $201.35   $201.40  
  Purchase #7 $231.89   12.653%   $261.231   $261.23   $261.25   $261.20  
  7 purchase totals = $865.83       $957.9030   $957.91   $957.90   $957.90