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 $95.79   7.344%   $102.8248   $102.82   $102.80   $102.80  
  Purchase #2 $64.68   11.739%   $72.2728   $72.27   $72.25   $72.30  
  Purchase #3 $14.70   3.640%   $15.2351   $15.24   $15.25   $15.20  
  Purchase #4 $107.83   8.852%   $117.3751   $117.38   $117.40   $117.40  
  Purchase #5 $145.87   8.436%   $158.1756   $158.18   $158.20   $158.20  
  Purchase #6 $84.30   6.568%   $89.8368   $89.84   $89.85   $89.80  
  Purchase #7 $78.44   8.306%   $84.9552   $84.96   $84.95   $85.00  
  7 purchase totals = $591.61       $640.6754   $640.69   $640.70   $640.70