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	$89.63	10.583%	$99.1155	$99.12	$99.10	$99.10
Purchase #2	$97.77	7.468%	$105.0715	$105.07	$105.05	$105.10
Purchase #3	$129.51	13.330%	$146.7737	$146.77	$146.75	$146.80
Purchase #4	$12.35	10.518%	$13.649	$13.65	$13.65	$13.60
Purchase #5	$100.77	10.630%	$111.4819	$111.48	$111.50	$111.50
Purchase #6	$6.49	4.260%	$6.7665	$6.77	$6.75	$6.80
Purchase #7	$49.87	11.523%	$55.6165	$55.62	$55.60	$55.60
7 purchase totals =	$486.39		$538.4746	$538.48	$538.40	$538.50