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	$239.64	7.704%	$258.1019	$258.10	$258.10	$258.10
Purchase #2	$50.71	13.300%	$57.4544	$57.45	$57.45	$57.50
Purchase #3	$223.88	5.244%	$235.6203	$235.62	$235.60	$235.60
Purchase #4	$156.50	10.244%	$172.5319	$172.53	$172.55	$172.50
Purchase #5	$79.40	13.566%	$90.1714	$90.17	$90.15	$90.20
Purchase #6	$165.91	3.753%	$172.1366	$172.14	$172.15	$172.10
Purchase #7	$203.89	10.794%	$225.8979	$225.90	$225.90	$225.90
7 purchase totals =	$1,119.93		$1,211.9144	$1,211.91	$1,211.90	$1,211.90