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 $23.27   11.799%   $26.0156   $26.02   $26.00   $26.00  
  Purchase #2 $184.76   4.581%   $193.2239   $193.22   $193.20   $193.20  
  Purchase #3 $109.46   8.709%   $118.9929   $118.99   $119.00   $119.00  
  Purchase #4 $178.61   4.586%   $186.8011   $186.80   $186.80   $186.80  
  Purchase #5 $194.84   7.639%   $209.7238   $209.72   $209.70   $209.70  
  Purchase #6 $103.60   13.308%   $117.3871   $117.39   $117.40   $117.40  
  Purchase #7 $50.30   13.516%   $57.0985   $57.10   $57.10   $57.10  
  7 purchase totals = $844.84       $909.2429   $909.24   $909.20   $909.20