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 $104.83   12.534%   $117.9694   $117.97   $117.95   $118.00  
  Purchase #2 $64.77   7.612%   $69.7003   $69.70   $69.70   $69.70  
  Purchase #3 $16.64   13.395%   $18.8689   $18.87   $18.85   $18.90  
  Purchase #4 $249.43   13.194%   $282.3398   $282.34   $282.35   $282.30  
  Purchase #5 $238.85   9.355%   $261.1944   $261.19   $261.20   $261.20  
  Purchase #6 $9.48   9.384%   $10.3696   $10.37   $10.35   $10.40  
  Purchase #7 $50.32   10.486%   $55.5966   $55.60   $55.60   $55.60  
  7 purchase totals = $734.32       $816.0390   $816.04   $816.00   $816.10