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	$145.77	13.633%	$165.6428	$165.64	$165.65	$165.60
Purchase #2	$30.28	12.188%	$33.9705	$33.97	$33.95	$34.00
Purchase #3	$224.39	4.865%	$235.3066	$235.31	$235.30	$235.30
Purchase #4	$82.70	10.261%	$91.1858	$91.19	$91.20	$91.20
Purchase #5	$165.31	9.505%	$181.0227	$181.02	$181.00	$181.00
Purchase #6	$137.81	4.145%	$143.5222	$143.52	$143.50	$143.50
Purchase #7	$68.84	13.360%	$78.037	$78.04	$78.05	$78.00
7 purchase totals =	$855.10		$928.6876	$928.69	$928.65	$928.60