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 $22.93   13.420%   $26.0072   $26.01   $26.00   $26.00  
  Purchase #2 $41.61   5.728%   $43.9934   $43.99   $44.00   $44.00  
  Purchase #3 $156.93   13.613%   $178.2929   $178.29   $178.30   $178.30  
  Purchase #4 $231.38   9.178%   $252.6161   $252.62   $252.60   $252.60  
  Purchase #5 $136.47   5.728%   $144.287   $144.29   $144.30   $144.30  
  Purchase #6 $78.98   4.443%   $82.4891   $82.49   $82.50   $82.50  
  Purchase #7 $67.83   12.106%   $76.0415   $76.04   $76.05   $76.00  
  7 purchase totals = $736.13       $803.7272   $803.73   $803.75   $803.70