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 $95.73   7.210%   $102.6321   $102.63   $102.65   $102.60  
  Purchase #2 $44.76   5.643%   $47.2858   $47.29   $47.30   $47.30  
  Purchase #3 $123.54   11.524%   $137.7767   $137.78   $137.80   $137.80  
  Purchase #4 $93.99   9.312%   $102.7423   $102.74   $102.75   $102.70  
  Purchase #5 $110.84   12.823%   $125.053   $125.05   $125.05   $125.10  
  Purchase #6 $84.98   7.151%   $91.0569   $91.06   $91.05   $91.10  
  Purchase #7 $27.63   9.420%   $30.2327   $30.23   $30.25   $30.20  
  7 purchase totals = $581.47       $636.7795   $636.78   $636.85   $636.80