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 $183.86   6.558%   $195.9175   $195.92   $195.90   $195.90  
  Purchase #2 $85.99   13.422%   $97.5316   $97.53   $97.55   $97.50  
  Purchase #3 $141.68   8.844%   $154.2102   $154.21   $154.20   $154.20  
  Purchase #4 $125.55   12.118%   $140.7641   $140.76   $140.75   $140.80  
  Purchase #5 $54.97   9.847%   $60.3829   $60.38   $60.40   $60.40  
  Purchase #6 $24.54   13.691%   $27.8998   $27.90   $27.90   $27.90  
  Purchase #7 $97.56   8.165%   $105.5258   $105.53   $105.55   $105.50  
  7 purchase totals = $714.15       $782.2319   $782.23   $782.25   $782.20