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 $147.94   4.502%   $154.6003   $154.60   $154.60   $154.60  
  Purchase #2 $231.39   11.366%   $257.6898   $257.69   $257.70   $257.70  
  Purchase #3 $13.68   3.427%   $14.1488   $14.15   $14.15   $14.10  
  Purchase #4 $74.29   12.761%   $83.7701   $83.77   $83.75   $83.80  
  Purchase #5 $48.25   5.584%   $50.9443   $50.94   $50.95   $50.90  
  Purchase #6 $164.37   5.338%   $173.1441   $173.14   $173.15   $173.10  
  Purchase #7 $125.88   12.695%   $141.8605   $141.86   $141.85   $141.90  
  7 purchase totals = $805.80       $876.1579   $876.15   $876.15   $876.10