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	$246.78	3.811%	$256.1848	$256.18	$256.20	$256.20
Purchase #2	$158.62	10.630%	$175.4813	$175.48	$175.50	$175.50
Purchase #3	$224.68	10.601%	$248.4983	$248.50	$248.50	$248.50
Purchase #4	$112.28	13.453%	$127.385	$127.39	$127.40	$127.40
Purchase #5	$235.63	9.674%	$258.4248	$258.42	$258.40	$258.40
Purchase #6	$244.37	4.226%	$254.6971	$254.70	$254.70	$254.70
Purchase #7	$174.41	12.721%	$196.5967	$196.60	$196.60	$196.60
7 purchase totals =	$1,396.77		$1,517.2680	$1,517.27	$1,517.30	$1,517.30