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 $68.84   11.768%   $76.9411   $76.94   $76.95   $76.90  
  Purchase #2 $139.30   10.854%   $154.4196   $154.42   $154.40   $154.40  
  Purchase #3 $140.76   4.286%   $146.793   $146.79   $146.80   $146.80  
  Purchase #4 $94.53   10.823%   $104.761   $104.76   $104.75   $104.80  
  Purchase #5 $58.32   12.707%   $65.7307   $65.73   $65.75   $65.70  
  Purchase #6 $241.74   9.526%   $264.7682   $264.77   $264.75   $264.80  
  Purchase #7 $29.76   5.256%   $31.3242   $31.32   $31.30   $31.30  
  7 purchase totals = $773.25       $844.7378   $844.73   $844.70   $844.70