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	$56.95	9.412%	$62.3101	$62.31	$62.30	$62.30
Purchase #2	$121.66	5.381%	$128.2065	$128.21	$128.20	$128.20
Purchase #3	$158.30	8.342%	$171.5054	$171.51	$171.50	$171.50
Purchase #4	$91.73	9.672%	$100.6021	$100.60	$100.60	$100.60
Purchase #5	$8.50	7.433%	$9.1318	$9.13	$9.15	$9.10
Purchase #6	$41.43	9.180%	$45.2333	$45.23	$45.25	$45.20
Purchase #7	$111.75	4.205%	$116.4491	$116.45	$116.45	$116.40
7 purchase totals =	$590.32		$633.4383	$633.44	$633.45	$633.30