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	$103.42	3.223%	$106.7532	$106.75	$106.75	$106.80
Purchase #2	$111.70	10.251%	$123.1504	$123.15	$123.15	$123.20
Purchase #3	$229.86	10.166%	$253.2276	$253.23	$253.25	$253.20
Purchase #4	$53.26	9.781%	$58.4694	$58.47	$58.45	$58.50
Purchase #5	$247.53	6.449%	$263.4932	$263.49	$263.50	$263.50
Purchase #6	$50.84	12.668%	$57.2804	$57.28	$57.30	$57.30
Purchase #7	$137.51	6.191%	$146.0232	$146.02	$146.00	$146.00
7 purchase totals =	$934.12		$1,008.3974	$1,008.39	$1,008.40	$1,008.50