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 $16.46   4.845%   $17.2575   $17.26   $17.25   $17.30  
  Purchase #2 $116.71   7.829%   $125.8472   $125.85   $125.85   $125.80  
  Purchase #3 $18.53   11.203%   $20.6059   $20.61   $20.60   $20.60  
  Purchase #4 $149.37   8.565%   $162.1635   $162.16   $162.15   $162.20  
  Purchase #5 $109.78   11.335%   $122.2236   $122.22   $122.20   $122.20  
  Purchase #6 $222.64   6.725%   $237.6125   $237.61   $237.60   $237.60  
  Purchase #7 $68.26   12.243%   $76.6171   $76.62   $76.60   $76.60  
  7 purchase totals = $701.75       $762.3273   $762.33   $762.25   $762.30