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 $75.92   8.772%   $82.5797   $82.58   $82.60   $82.60  
  Purchase #2 $115.77   4.764%   $121.2853   $121.29   $121.30   $121.30  
  Purchase #3 $158.42   5.440%   $167.038   $167.04   $167.05   $167.00  
  Purchase #4 $200.55   8.853%   $218.3047   $218.30   $218.30   $218.30  
  Purchase #5 $123.47   4.755%   $129.341   $129.34   $129.35   $129.30  
  Purchase #6 $66.86   8.475%   $72.5264   $72.53   $72.55   $72.50  
  Purchase #7 $127.49   8.602%   $138.4567   $138.46   $138.45   $138.50  
  7 purchase totals = $868.48       $929.5318   $929.54   $929.60   $929.50