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 $76.43   10.752%   $84.6478   $84.65   $84.65   $84.60  
  Purchase #2 $158.69   9.214%   $173.3117   $173.31   $173.30   $173.30  
  Purchase #3 $81.77   11.608%   $91.2619   $91.26   $91.25   $91.30  
  Purchase #4 $204.69   6.123%   $217.2232   $217.22   $217.20   $217.20  
  Purchase #5 $38.84   5.206%   $40.862   $40.86   $40.85   $40.90  
  Purchase #6 $219.46   13.386%   $248.8369   $248.84   $248.85   $248.80  
  Purchase #7 $95.26   13.608%   $108.223   $108.22   $108.20   $108.20  
  7 purchase totals = $875.14       $964.3665   $964.36   $964.30   $964.30