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 $109.82   10.635%   $121.4994   $121.50   $121.50   $121.50  
  Purchase #2 $173.46   10.601%   $191.8485   $191.85   $191.85   $191.80  
  Purchase #3 $62.64   11.226%   $69.672   $69.67   $69.65   $69.70  
  Purchase #4 $103.45   13.333%   $117.243   $117.24   $117.25   $117.20  
  Purchase #5 $109.95   7.486%   $118.1809   $118.18   $118.20   $118.20  
  Purchase #6 $173.28   5.263%   $182.3997   $182.40   $182.40   $182.40  
  Purchase #7 $248.67   7.126%   $266.3902   $266.39   $266.40   $266.40  
  7 purchase totals = $981.27       $1,067.2337   $1,067.23   $1,067.25   $1,067.20