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 $77.78   5.726%   $82.2337   $82.23   $82.25   $82.20  
  Purchase #2 $130.63   4.789%   $136.8859   $136.89   $136.90   $136.90  
  Purchase #3 $155.95   3.563%   $161.5065   $161.51   $161.50   $161.50  
  Purchase #4 $186.84   8.295%   $202.3384   $202.34   $202.35   $202.30  
  Purchase #5 $88.38   8.853%   $96.2043   $96.20   $96.20   $96.20  
  Purchase #6 $101.69   6.801%   $108.6059   $108.61   $108.60   $108.60  
  Purchase #7 $111.33   6.849%   $118.955   $118.96   $118.95   $119.00  
  7 purchase totals = $852.60       $906.7297   $906.74   $906.75   $906.70