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	$157.82	9.185%	$172.3158	$172.32	$172.30	$172.30
Purchase #2	$157.70	5.225%	$165.9398	$165.94	$165.95	$165.90
Purchase #3	$21.33	10.874%	$23.6494	$23.65	$23.65	$23.60
Purchase #4	$36.51	10.579%	$40.3724	$40.37	$40.35	$40.40
Purchase #5	$58.71	9.831%	$64.4818	$64.48	$64.50	$64.50
Purchase #6	$37.45	13.150%	$42.3747	$42.37	$42.35	$42.40
Purchase #7	$17.43	10.406%	$19.2438	$19.24	$19.25	$19.20
7 purchase totals =	$486.95		$528.3777	$528.37	$528.35	$528.30