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 $91.50   3.325%   $94.5424   $94.54   $94.55   $94.50  
  Purchase #2 $130.53   8.226%   $141.2674   $141.27   $141.25   $141.30  
  Purchase #3 $141.34   7.746%   $152.2882   $152.29   $152.30   $152.30  
  Purchase #4 $193.79   12.219%   $217.4692   $217.47   $217.45   $217.50  
  Purchase #5 $139.51   13.114%   $157.8053   $157.81   $157.80   $157.80  
  Purchase #6 $145.51   12.333%   $163.4557   $163.46   $163.45   $163.50  
  Purchase #7 $24.69   12.867%   $27.8669   $27.87   $27.85   $27.90  
  7 purchase totals = $866.87       $954.6951   $954.71   $954.65   $954.80