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	$106.91	6.240%	$113.5812	$113.58	$113.60	$113.60
Purchase #2	$101.83	4.295%	$106.2036	$106.20	$106.20	$106.20
Purchase #3	$142.27	6.235%	$151.1405	$151.14	$151.15	$151.10
Purchase #4	$159.58	4.339%	$166.5042	$166.50	$166.50	$166.50
Purchase #5	$44.25	13.367%	$50.1649	$50.16	$50.15	$50.20
Purchase #6	$33.42	11.675%	$37.3218	$37.32	$37.30	$37.30
Purchase #7	$34.80	7.397%	$37.3742	$37.37	$37.35	$37.40
7 purchase totals =	$623.06		$662.2904	$662.27	$662.25	$662.30