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	$223.33	6.698%	$238.2886	$238.29	$238.30	$238.30
Purchase #2	$239.73	13.485%	$272.0576	$272.06	$272.05	$272.10
Purchase #3	$170.89	11.353%	$190.2911	$190.29	$190.30	$190.30
Purchase #4	$120.77	13.718%	$137.3372	$137.34	$137.35	$137.30
Purchase #5	$159.90	8.533%	$173.5443	$173.54	$173.55	$173.50
Purchase #6	$131.26	11.294%	$146.0845	$146.08	$146.10	$146.10
Purchase #7	$193.61	13.558%	$219.8596	$219.86	$219.85	$219.90
7 purchase totals =	$1,239.49		$1,377.4629	$1,377.46	$1,377.50	$1,377.50