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 $111.61   11.220%   $124.1326   $124.13   $124.15   $124.10  
  Purchase #2 $53.93   11.807%   $60.2975   $60.30   $60.30   $60.30  
  Purchase #3 $194.46   5.242%   $204.6536   $204.65   $204.65   $204.70  
  Purchase #4 $105.55   11.738%   $117.9395   $117.94   $117.95   $117.90  
  Purchase #5 $85.62   5.748%   $90.5414   $90.54   $90.55   $90.50  
  Purchase #6 $176.57   3.246%   $182.3015   $182.30   $182.30   $182.30  
  Purchase #7 $38.31   8.219%   $41.4587   $41.46   $41.45   $41.50  
  7 purchase totals = $766.05       $821.3248   $821.32   $821.35   $821.30