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 $245.97   7.454%   $264.3046   $264.30   $264.30   $264.30  
  Purchase #2 $171.73   7.742%   $185.0253   $185.03   $185.05   $185.00  
  Purchase #3 $48.70   11.715%   $54.4052   $54.41   $54.40   $54.40  
  Purchase #4 $58.40   5.614%   $61.6786   $61.68   $61.70   $61.70  
  Purchase #5 $146.31   8.514%   $158.7668   $158.77   $158.75   $158.80  
  Purchase #6 $156.63   12.648%   $176.4406   $176.44   $176.45   $176.40  
  Purchase #7 $84.35   9.118%   $92.041   $92.04   $92.05   $92.00  
  7 purchase totals = $912.09       $992.6621   $992.67   $992.70   $992.60