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 $231.35   4.173%   $241.0042   $241.00   $241.00   $241.00  
  Purchase #2 $167.91   5.326%   $176.8529   $176.85   $176.85   $176.90  
  Purchase #3 $18.41   10.361%   $20.3175   $20.32   $20.30   $20.30  
  Purchase #4 $25.46   9.794%   $27.9536   $27.95   $27.95   $28.00  
  Purchase #5 $199.95   12.177%   $224.2979   $224.30   $224.30   $224.30  
  Purchase #6 $93.38   12.107%   $104.6855   $104.69   $104.70   $104.70  
  Purchase #7 $16.29   8.216%   $17.6284   $17.63   $17.65   $17.60  
  7 purchase totals = $752.75       $812.7400   $812.74   $812.75   $812.80