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	$89.72	12.145%	$100.6165	$100.62	$100.60	$100.60
Purchase #2	$235.76	11.527%	$262.9361	$262.94	$262.95	$262.90
Purchase #3	$141.51	12.824%	$159.6572	$159.66	$159.65	$159.70
Purchase #4	$115.37	13.690%	$131.1642	$131.16	$131.15	$131.20
Purchase #5	$146.80	4.411%	$153.2753	$153.28	$153.30	$153.30
Purchase #6	$46.28	6.357%	$49.222	$49.22	$49.20	$49.20
Purchase #7	$36.56	5.310%	$38.5013	$38.50	$38.50	$38.50
7 purchase totals =	$812.00		$895.3726	$895.38	$895.35	$895.40