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 $55.76   9.423%   $61.0143   $61.01   $61.00   $61.00  
  Purchase #2 $125.41   3.127%   $129.3316   $129.33   $129.35   $129.30  
  Purchase #3 $104.38   8.660%   $113.4193   $113.42   $113.40   $113.40  
  Purchase #4 $131.44   13.760%   $149.5261   $149.53   $149.55   $149.50  
  Purchase #5 $153.59   5.425%   $161.9223   $161.92   $161.90   $161.90  
  Purchase #6 $226.68   8.190%   $245.2451   $245.25   $245.25   $245.20  
  Purchase #7 $73.32   4.865%   $76.887   $76.89   $76.90   $76.90  
  7 purchase totals = $870.58       $937.3457   $937.35   $937.35   $937.20