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	$47.99	11.728%	$53.6183	$53.62	$53.60	$53.60
Purchase #2	$55.37	7.501%	$59.5233	$59.52	$59.50	$59.50
Purchase #3	$152.62	8.159%	$165.0723	$165.07	$165.05	$165.10
Purchase #4	$110.49	10.784%	$122.4052	$122.41	$122.40	$122.40
Purchase #5	$80.78	9.717%	$88.6294	$88.63	$88.65	$88.60
Purchase #6	$91.32	4.702%	$95.6139	$95.61	$95.60	$95.60
Purchase #7	$21.71	4.359%	$22.6563	$22.66	$22.65	$22.70
7 purchase totals =	$560.28		$607.5187	$607.52	$607.45	$607.50