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	$77.83	4.600%	$81.4102	$81.41	$81.40	$81.40
Purchase #2	$60.89	11.458%	$67.8668	$67.87	$67.85	$67.90
Purchase #3	$117.28	11.287%	$130.5174	$130.52	$130.50	$130.50
Purchase #4	$65.79	11.764%	$73.5295	$73.53	$73.55	$73.50
Purchase #5	$69.68	10.740%	$77.1636	$77.16	$77.15	$77.20
Purchase #6	$217.32	9.109%	$237.1157	$237.12	$237.10	$237.10
Purchase #7	$66.81	6.374%	$71.0685	$71.07	$71.05	$71.10
7 purchase totals =	$675.60		$738.6717	$738.68	$738.60	$738.70