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 $174.56   11.723%   $195.0237   $195.02   $195.00   $195.00  
  Purchase #2 $71.48   6.802%   $76.3421   $76.34   $76.35   $76.30  
  Purchase #3 $47.37   4.570%   $49.5348   $49.53   $49.55   $49.50  
  Purchase #4 $237.42   7.807%   $255.9554   $255.96   $255.95   $256.00  
  Purchase #5 $192.51   8.640%   $209.1429   $209.14   $209.15   $209.10  
  Purchase #6 $159.91   6.538%   $170.3649   $170.36   $170.35   $170.40  
  Purchase #7 $248.39   8.267%   $268.9244   $268.92   $268.90   $268.90  
  7 purchase totals = $1,131.64       $1,225.2882   $1,225.27   $1,225.25   $1,225.20