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	$136.39	12.292%	$153.1551	$153.16	$153.15	$153.20
Purchase #2	$49.64	6.823%	$53.0269	$53.03	$53.05	$53.00
Purchase #3	$80.86	11.259%	$89.964	$89.96	$89.95	$90.00
Purchase #4	$157.52	4.743%	$164.9912	$164.99	$165.00	$165.00
Purchase #5	$75.88	9.228%	$82.8822	$82.88	$82.90	$82.90
Purchase #6	$145.45	9.408%	$159.1339	$159.13	$159.15	$159.10
Purchase #7	$46.89	13.385%	$53.1662	$53.17	$53.15	$53.20
7 purchase totals =	$692.63		$756.3195	$756.32	$756.35	$756.40