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 $244.56   11.223%   $272.007   $272.01   $272.00   $272.00  
  Purchase #2 $93.43   4.390%   $97.5316   $97.53   $97.55   $97.50  
  Purchase #3 $21.51   5.569%   $22.7079   $22.71   $22.70   $22.70  
  Purchase #4 $139.65   9.752%   $153.2687   $153.27   $153.25   $153.30  
  Purchase #5 $224.95   9.126%   $245.4789   $245.48   $245.50   $245.50  
  Purchase #6 $50.63   12.333%   $56.8742   $56.87   $56.85   $56.90  
  Purchase #7 $25.94   12.378%   $29.1509   $29.15   $29.15   $29.20  
  7 purchase totals = $800.67       $877.0192   $877.02   $877.00   $877.10