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	$231.68	13.832%	$263.726	$263.73	$263.75	$263.70
Purchase #2	$159.79	4.419%	$166.8511	$166.85	$166.85	$166.90
Purchase #3	$118.61	9.723%	$130.1425	$130.14	$130.15	$130.10
Purchase #4	$100.25	12.333%	$112.6138	$112.61	$112.60	$112.60
Purchase #5	$10.93	13.200%	$12.3728	$12.37	$12.35	$12.40
Purchase #6	$29.61	13.581%	$33.6313	$33.63	$33.65	$33.60
Purchase #7	$20.95	7.336%	$22.4869	$22.49	$22.50	$22.50
7 purchase totals =	$671.82		$741.8244	$741.82	$741.85	$741.80