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 $164.69   3.846%   $171.024   $171.02   $171.00   $171.00  
  Purchase #2 $175.83   3.560%   $182.0895   $182.09   $182.10   $182.10  
  Purchase #3 $66.47   5.137%   $69.8846   $69.88   $69.90   $69.90  
  Purchase #4 $133.95   9.357%   $146.4837   $146.48   $146.50   $146.50  
  Purchase #5 $76.34   9.563%   $83.6404   $83.64   $83.65   $83.60  
  Purchase #6 $88.26   12.168%   $98.9995   $99.00   $99.00   $99.00  
  Purchase #7 $199.53   6.198%   $211.8969   $211.90   $211.90   $211.90  
  7 purchase totals = $905.07       $964.0186   $964.01   $964.05   $964.00