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	$43.48	13.283%	$49.2554	$49.26	$49.25	$49.30
Purchase #2	$34.38	4.376%	$35.8845	$35.88	$35.90	$35.90
Purchase #3	$190.48	8.240%	$206.1756	$206.18	$206.20	$206.20
Purchase #4	$139.78	11.172%	$155.3962	$155.40	$155.40	$155.40
Purchase #5	$40.55	7.141%	$43.4457	$43.45	$43.45	$43.40
Purchase #6	$30.64	9.634%	$33.5919	$33.59	$33.60	$33.60
Purchase #7	$168.61	10.662%	$186.5872	$186.59	$186.60	$186.60
7 purchase totals =	$647.92		$710.3365	$710.35	$710.40	$710.40