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 $66.38   13.273%   $75.1906   $75.19   $75.20   $75.20  
  Purchase #2 $249.94   5.686%   $264.1516   $264.15   $264.15   $264.20  
  Purchase #3 $53.41   10.104%   $58.8065   $58.81   $58.80   $58.80  
  Purchase #4 $199.32   11.295%   $221.8332   $221.83   $221.85   $221.80  
  Purchase #5 $9.74   9.792%   $10.6937   $10.69   $10.70   $10.70  
  Purchase #6 $39.99   10.644%   $44.2465   $44.25   $44.25   $44.20  
  Purchase #7 $46.74   7.420%   $50.2081   $50.21   $50.20   $50.20  
  7 purchase totals = $665.52       $725.1302   $725.13   $725.15   $725.10