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	$226.54	3.482%	$234.4281	$234.43	$234.45	$234.40
Purchase #2	$98.58	12.463%	$110.866	$110.87	$110.85	$110.90
Purchase #3	$44.50	3.201%	$45.9244	$45.92	$45.90	$45.90
Purchase #4	$165.95	4.619%	$173.6152	$173.62	$173.60	$173.60
Purchase #5	$91.43	13.119%	$103.4247	$103.42	$103.40	$103.40
Purchase #6	$159.62	7.790%	$172.0544	$172.05	$172.05	$172.10
Purchase #7	$115.97	12.605%	$130.588	$130.59	$130.60	$130.60
7 purchase totals =	$902.59		$970.9008	$970.90	$970.85	$970.90