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	$13.69	13.113%	$15.4852	$15.49	$15.50	$15.50
Purchase #2	$137.51	10.575%	$152.0517	$152.05	$152.05	$152.10
Purchase #3	$53.58	3.393%	$55.398	$55.40	$55.40	$55.40
Purchase #4	$45.31	9.685%	$49.6983	$49.70	$49.70	$49.70
Purchase #5	$53.25	7.174%	$57.0702	$57.07	$57.05	$57.10
Purchase #6	$35.79	3.394%	$37.0047	$37.00	$37.00	$37.00
Purchase #7	$165.69	4.487%	$173.1245	$173.12	$173.10	$173.10
7 purchase totals =	$504.82		$539.8326	$539.83	$539.80	$539.90