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	$216.78	12.747%	$244.4129	$244.41	$244.40	$244.40
Purchase #2	$29.58	3.841%	$30.7162	$30.72	$30.70	$30.70
Purchase #3	$99.85	3.607%	$103.4516	$103.45	$103.45	$103.50
Purchase #4	$54.87	12.750%	$61.8659	$61.87	$61.85	$61.90
Purchase #5	$119.55	8.874%	$130.1589	$130.16	$130.15	$130.20
Purchase #6	$61.31	7.412%	$65.8543	$65.85	$65.85	$65.90
Purchase #7	$36.78	10.673%	$40.7055	$40.71	$40.70	$40.70
7 purchase totals =	$618.72		$677.1653	$677.17	$677.10	$677.30