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 $43.57   6.228%   $46.2835   $46.28   $46.30   $46.30  
  Purchase #2 $117.83   5.423%   $124.2199   $124.22   $124.20   $124.20  
  Purchase #3 $109.38   11.130%   $121.554   $121.55   $121.55   $121.60  
  Purchase #4 $243.76   3.277%   $251.748   $251.75   $251.75   $251.70  
  Purchase #5 $61.40   5.489%   $64.7702   $64.77   $64.75   $64.80  
  Purchase #6 $158.30   4.394%   $165.2557   $165.26   $165.25   $165.30  
  Purchase #7 $44.49   10.812%   $49.3003   $49.30   $49.30   $49.30  
  7 purchase totals = $778.73       $823.1316   $823.13   $823.10   $823.20