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 $54.64   13.557%   $62.0475   $62.05   $62.05   $62.00  
  Purchase #2 $95.71   13.759%   $108.8787   $108.88   $108.90   $108.90  
  Purchase #3 $40.32   4.618%   $42.182   $42.18   $42.20   $42.20  
  Purchase #4 $146.93   5.816%   $155.4754   $155.48   $155.50   $155.50  
  Purchase #5 $84.50   8.588%   $91.7569   $91.76   $91.75   $91.80  
  Purchase #6 $113.74   5.835%   $120.3767   $120.38   $120.40   $120.40  
  Purchase #7 $93.28   11.470%   $103.9792   $103.98   $104.00   $104.00  
  7 purchase totals = $629.12       $684.6964   $684.71   $684.80   $684.80