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	$99.52	12.326%	$111.7868	$111.79	$111.80	$111.80
Purchase #2	$100.35	9.360%	$109.7428	$109.74	$109.75	$109.70
Purchase #3	$111.57	13.455%	$126.5817	$126.58	$126.60	$126.60
Purchase #4	$20.35	7.129%	$21.8008	$21.80	$21.80	$21.80
Purchase #5	$126.43	13.204%	$143.1238	$143.12	$143.10	$143.10
Purchase #6	$194.88	13.721%	$221.6195	$221.62	$221.60	$221.60
Purchase #7	$24.48	13.422%	$27.7657	$27.77	$27.75	$27.80
7 purchase totals =	$677.58		$762.4211	$762.42	$762.40	$762.40