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	$236.51	5.457%	$249.4164	$249.42	$249.40	$249.40
Purchase #2	$248.55	7.318%	$266.7389	$266.74	$266.75	$266.70
Purchase #3	$105.43	5.381%	$111.1032	$111.10	$111.10	$111.10
Purchase #4	$92.27	13.481%	$104.7089	$104.71	$104.70	$104.70
Purchase #5	$184.42	6.764%	$196.8942	$196.89	$196.90	$196.90
Purchase #6	$177.32	8.194%	$191.8496	$191.85	$191.85	$191.80
Purchase #7	$238.76	12.754%	$269.2115	$269.21	$269.20	$269.20
7 purchase totals =	$1,283.26		$1,389.9227	$1,389.92	$1,389.90	$1,389.80