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	$15.35	3.390%	$15.8704	$15.87	$15.85	$15.90
Purchase #2	$221.38	7.718%	$238.4661	$238.47	$238.45	$238.50
Purchase #3	$146.84	12.548%	$165.2655	$165.27	$165.25	$165.30
Purchase #4	$66.89	3.192%	$69.0251	$69.03	$69.05	$69.00
Purchase #5	$230.27	12.205%	$258.3745	$258.37	$258.35	$258.40
Purchase #6	$74.37	12.493%	$83.661	$83.66	$83.65	$83.70
Purchase #7	$200.50	12.575%	$225.7129	$225.71	$225.70	$225.70
7 purchase totals =	$955.60		$1,056.3755	$1,056.38	$1,056.30	$1,056.50