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	$143.29	5.599%	$151.3128	$151.31	$151.30	$151.30
Purchase #2	$167.25	7.515%	$179.8188	$179.82	$179.80	$179.80
Purchase #3	$56.35	8.490%	$61.1341	$61.13	$61.15	$61.10
Purchase #4	$94.41	7.294%	$101.2963	$101.30	$101.30	$101.30
Purchase #5	$50.62	7.433%	$54.3826	$54.38	$54.40	$54.40
Purchase #6	$105.92	5.438%	$111.6799	$111.68	$111.70	$111.70
Purchase #7	$175.65	5.204%	$184.7908	$184.79	$184.80	$184.80
7 purchase totals =	$793.49		$844.4153	$844.41	$844.45	$844.40