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 $60.27   10.772%   $66.7623   $66.76   $66.75   $66.80  
  Purchase #2 $75.31   8.805%   $81.941   $81.94   $81.95   $81.90  
  Purchase #3 $239.69   13.406%   $271.8228   $271.82   $271.80   $271.80  
  Purchase #4 $194.80   7.659%   $209.7197   $209.72   $209.70   $209.70  
  Purchase #5 $236.59   5.367%   $249.2878   $249.29   $249.30   $249.30  
  Purchase #6 $33.78   5.853%   $35.7571   $35.76   $35.75   $35.80  
  Purchase #7 $10.26   7.388%   $11.018   $11.02   $11.00   $11.00  
  7 purchase totals = $850.70       $926.3087   $926.31   $926.25   $926.30