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	$208.83	4.422%	$218.0645	$218.06	$218.05	$218.10
Purchase #2	$137.61	6.329%	$146.3193	$146.32	$146.30	$146.30
Purchase #3	$72.32	13.162%	$81.8388	$81.84	$81.85	$81.80
Purchase #4	$53.72	9.113%	$58.6155	$58.62	$58.60	$58.60
Purchase #5	$47.37	7.114%	$50.7399	$50.74	$50.75	$50.70
Purchase #6	$59.85	7.426%	$64.2945	$64.29	$64.30	$64.30
Purchase #7	$47.58	12.726%	$53.635	$53.64	$53.65	$53.60
7 purchase totals =	$627.28		$673.5075	$673.51	$673.50	$673.40