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	$40.56	11.606%	$45.2674	$45.27	$45.25	$45.30
Purchase #2	$63.73	13.388%	$72.2622	$72.26	$72.25	$72.30
Purchase #3	$122.86	11.576%	$137.0823	$137.08	$137.10	$137.10
Purchase #4	$35.92	13.240%	$40.6758	$40.68	$40.70	$40.70
Purchase #5	$51.55	3.226%	$53.213	$53.21	$53.20	$53.20
Purchase #6	$100.57	7.682%	$108.2958	$108.30	$108.30	$108.30
Purchase #7	$165.56	5.623%	$174.8694	$174.87	$174.85	$174.90
7 purchase totals =	$580.75		$631.6659	$631.67	$631.65	$631.80