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 $64.44   13.474%   $73.1226   $73.12   $73.10   $73.10  
  Purchase #2 $157.36   10.251%   $173.491   $173.49   $173.50   $173.50  
  Purchase #3 $69.39   6.639%   $73.9968   $74.00   $74.00   $74.00  
  Purchase #4 $95.46   9.182%   $104.2251   $104.23   $104.25   $104.20  
  Purchase #5 $249.70   4.159%   $260.085   $260.09   $260.10   $260.10  
  Purchase #6 $47.56   7.246%   $51.0062   $51.01   $51.00   $51.00  
  Purchase #7 $200.84   13.185%   $227.3208   $227.32   $227.30   $227.30  
  7 purchase totals = $884.75       $963.2475   $963.26   $963.25   $963.20