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	$86.95	10.770%	$96.3145	$96.31	$96.30	$96.30
Purchase #2	$238.94	9.120%	$260.7313	$260.73	$260.75	$260.70
Purchase #3	$120.80	5.332%	$127.2411	$127.24	$127.25	$127.20
Purchase #4	$141.54	3.733%	$146.8237	$146.82	$146.80	$146.80
Purchase #5	$18.58	8.289%	$20.1201	$20.12	$20.10	$20.10
Purchase #6	$227.61	12.742%	$256.6121	$256.61	$256.60	$256.60
Purchase #7	$171.62	12.371%	$192.8511	$192.85	$192.85	$192.90
7 purchase totals =	$1,006.04		$1,100.6939	$1,100.68	$1,100.65	$1,100.60