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	$124.40	11.851%	$139.1426	$139.14	$139.15	$139.10
Purchase #2	$158.96	5.341%	$167.4501	$167.45	$167.45	$167.50
Purchase #3	$53.72	8.396%	$58.2303	$58.23	$58.25	$58.20
Purchase #4	$20.26	10.135%	$22.3134	$22.31	$22.30	$22.30
Purchase #5	$115.78	13.820%	$131.7808	$131.78	$131.80	$131.80
Purchase #6	$184.97	8.300%	$200.3225	$200.32	$200.30	$200.30
Purchase #7	$158.43	8.579%	$172.0217	$172.02	$172.00	$172.00
7 purchase totals =	$816.52		$891.2614	$891.25	$891.25	$891.20