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	$145.92	8.491%	$158.3101	$158.31	$158.30	$158.30
Purchase #2	$125.77	3.856%	$130.6197	$130.62	$130.60	$130.60
Purchase #3	$155.34	11.158%	$172.6728	$172.67	$172.65	$172.70
Purchase #4	$81.65	10.723%	$90.4053	$90.41	$90.40	$90.40
Purchase #5	$34.73	8.712%	$37.7557	$37.76	$37.75	$37.80
Purchase #6	$41.44	7.213%	$44.4291	$44.43	$44.45	$44.40
Purchase #7	$27.84	8.337%	$30.161	$30.16	$30.15	$30.20
7 purchase totals =	$612.69		$664.3537	$664.36	$664.30	$664.40