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	$47.67	11.230%	$53.0233	$53.02	$53.00	$53.00
Purchase #2	$158.75	9.439%	$173.7344	$173.73	$173.75	$173.70
Purchase #3	$72.59	10.411%	$80.1473	$80.15	$80.15	$80.10
Purchase #4	$22.89	6.331%	$24.3392	$24.34	$24.35	$24.30
Purchase #5	$11.25	11.245%	$12.5151	$12.52	$12.50	$12.50
Purchase #6	$74.79	4.443%	$78.1129	$78.11	$78.10	$78.10
Purchase #7	$52.67	10.621%	$58.2641	$58.26	$58.25	$58.30
7 purchase totals =	$440.61		$480.1363	$480.13	$480.10	$480.00