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 $61.32   12.135%   $68.7612   $68.76   $68.75   $68.80  
  Purchase #2 $68.38   8.601%   $74.2614   $74.26   $74.25   $74.30  
  Purchase #3 $117.48   6.418%   $125.0199   $125.02   $125.00   $125.00  
  Purchase #4 $93.72   5.303%   $98.69   $98.69   $98.70   $98.70  
  Purchase #5 $207.36   4.697%   $217.0997   $217.10   $217.10   $217.10  
  Purchase #6 $168.80   10.714%   $186.8852   $186.89   $186.90   $186.90  
  Purchase #7 $109.58   3.867%   $113.8175   $113.82   $113.80   $113.80  
  7 purchase totals = $826.64       $884.5349   $884.54   $884.50   $884.60