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	$153.86	12.118%	$172.5048	$172.50	$172.50	$172.50
Purchase #2	$52.60	10.110%	$57.9179	$57.92	$57.90	$57.90
Purchase #3	$35.68	10.667%	$39.486	$39.49	$39.50	$39.50
Purchase #4	$246.85	12.467%	$277.6248	$277.62	$277.60	$277.60
Purchase #5	$18.40	12.405%	$20.6825	$20.68	$20.70	$20.70
Purchase #6	$159.82	8.497%	$173.3999	$173.40	$173.40	$173.40
Purchase #7	$142.40	11.624%	$158.9526	$158.95	$158.95	$159.00
7 purchase totals =	$809.61		$900.5685	$900.56	$900.55	$900.60