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	$154.37	3.578%	$159.8934	$159.89	$159.90	$159.90
Purchase #2	$78.52	5.362%	$82.7302	$82.73	$82.75	$82.70
Purchase #3	$187.52	13.271%	$212.4058	$212.41	$212.40	$212.40
Purchase #4	$100.51	11.110%	$111.6767	$111.68	$111.70	$111.70
Purchase #5	$248.91	3.662%	$258.0251	$258.03	$258.05	$258.00
Purchase #6	$223.66	6.562%	$238.3366	$238.34	$238.35	$238.30
Purchase #7	$55.65	8.206%	$60.2166	$60.22	$60.20	$60.20
7 purchase totals =	$1,049.14		$1,123.2844	$1,123.30	$1,123.35	$1,123.20