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	$120.69	3.840%	$125.3245	$125.32	$125.30	$125.30
Purchase #2	$37.27	13.281%	$42.2198	$42.22	$42.20	$42.20
Purchase #3	$124.48	3.672%	$129.0509	$129.05	$129.05	$129.10
Purchase #4	$213.63	9.388%	$233.6856	$233.69	$233.70	$233.70
Purchase #5	$90.68	10.847%	$100.5161	$100.52	$100.50	$100.50
Purchase #6	$153.61	7.614%	$165.3059	$165.31	$165.30	$165.30
Purchase #7	$156.31	10.803%	$173.1962	$173.20	$173.20	$173.20
7 purchase totals =	$896.67		$969.2990	$969.31	$969.25	$969.30