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	$63.68	4.582%	$66.5978	$66.60	$66.60	$66.60
Purchase #2	$154.56	7.572%	$166.2633	$166.26	$166.25	$166.30
Purchase #3	$26.48	8.204%	$28.6524	$28.65	$28.65	$28.70
Purchase #4	$97.34	4.238%	$101.4653	$101.47	$101.45	$101.50
Purchase #5	$244.60	4.410%	$255.3869	$255.39	$255.40	$255.40
Purchase #6	$204.82	10.237%	$225.7874	$225.79	$225.80	$225.80
Purchase #7	$112.99	12.554%	$127.1748	$127.17	$127.15	$127.20
7 purchase totals =	$904.47		$971.3279	$971.33	$971.30	$971.50