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 $30.76   11.857%   $34.4072   $34.41   $34.40   $34.40  
  Purchase #2 $104.73   13.546%   $118.9167   $118.92   $118.90   $118.90  
  Purchase #3 $110.65   13.845%   $125.9695   $125.97   $125.95   $126.00  
  Purchase #4 $69.60   6.473%   $74.1052   $74.11   $74.10   $74.10  
  Purchase #5 $75.66   11.342%   $84.2414   $84.24   $84.25   $84.20  
  Purchase #6 $171.57   11.306%   $190.9677   $190.97   $190.95   $191.00  
  Purchase #7 $192.66   7.341%   $206.8032   $206.80   $206.80   $206.80  
  7 purchase totals = $755.63       $835.4109   $835.42   $835.35   $835.40