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	$134.50	7.422%	$144.4826	$144.48	$144.50	$144.50
Purchase #2	$231.67	9.421%	$253.4956	$253.50	$253.50	$253.50
Purchase #3	$17.52	5.678%	$18.5148	$18.51	$18.50	$18.50
Purchase #4	$129.77	12.756%	$146.3235	$146.32	$146.30	$146.30
Purchase #5	$140.56	9.664%	$154.1437	$154.14	$154.15	$154.10
Purchase #6	$238.43	7.389%	$256.0476	$256.05	$256.05	$256.00
Purchase #7	$176.35	5.400%	$185.8729	$185.87	$185.85	$185.90
7 purchase totals =	$1,068.80		$1,158.8807	$1,158.87	$1,158.85	$1,158.80