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	$49.90	10.279%	$55.0292	$55.03	$55.05	$55.00
Purchase #2	$41.81	8.469%	$45.3509	$45.35	$45.35	$45.40
Purchase #3	$145.85	13.597%	$165.6812	$165.68	$165.70	$165.70
Purchase #4	$77.74	12.580%	$87.5197	$87.52	$87.50	$87.50
Purchase #5	$80.95	13.159%	$91.6022	$91.60	$91.60	$91.60
Purchase #6	$231.52	10.633%	$256.1375	$256.14	$256.15	$256.10
Purchase #7	$96.29	4.528%	$100.65	$100.65	$100.65	$100.70
7 purchase totals =	$724.06		$801.9707	$801.97	$802.00	$802.00