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	$146.96	13.275%	$166.4689	$166.47	$166.45	$166.50
Purchase #2	$151.96	4.442%	$158.7101	$158.71	$158.70	$158.70
Purchase #3	$205.31	13.535%	$233.0987	$233.10	$233.10	$233.10
Purchase #4	$128.67	12.115%	$144.2584	$144.26	$144.25	$144.30
Purchase #5	$68.73	4.297%	$71.6833	$71.68	$71.70	$71.70
Purchase #6	$16.28	6.344%	$17.3128	$17.31	$17.30	$17.30
Purchase #7	$49.99	6.675%	$53.3268	$53.33	$53.35	$53.30
7 purchase totals =	$767.90		$844.8590	$844.86	$844.85	$844.90