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 $93.53   3.497%   $96.8007   $96.80   $96.80   $96.80  
  Purchase #2 $209.55   7.548%   $225.3668   $225.37   $225.35   $225.40  
  Purchase #3 $116.62   7.844%   $125.7677   $125.77   $125.75   $125.80  
  Purchase #4 $101.33   11.140%   $112.6182   $112.62   $112.60   $112.60  
  Purchase #5 $204.71   3.625%   $212.1307   $212.13   $212.15   $212.10  
  Purchase #6 $160.35   11.794%   $179.2617   $179.26   $179.25   $179.30  
  Purchase #7 $88.72   4.226%   $92.4693   $92.47   $92.45   $92.50  
  7 purchase totals = $974.81       $1,044.4151   $1,044.42   $1,044.35   $1,044.50