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	$131.71	11.143%	$146.3864	$146.39	$146.40	$146.40
Purchase #2	$94.86	5.874%	$100.4321	$100.43	$100.45	$100.40
Purchase #3	$10.96	11.873%	$12.2613	$12.26	$12.25	$12.30
Purchase #4	$228.49	10.169%	$251.7251	$251.73	$251.75	$251.70
Purchase #5	$48.46	13.220%	$54.8664	$54.87	$54.85	$54.90
Purchase #6	$146.30	4.166%	$152.3949	$152.39	$152.40	$152.40
Purchase #7	$19.57	3.850%	$20.3234	$20.32	$20.30	$20.30
7 purchase totals =	$680.35		$738.3896	$738.39	$738.40	$738.40