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	$105.28	5.787%	$111.3726	$111.37	$111.35	$111.40
Purchase #2	$128.72	11.809%	$143.9205	$143.92	$143.90	$143.90
Purchase #3	$247.49	6.670%	$263.9976	$264.00	$264.00	$264.00
Purchase #4	$91.51	3.181%	$94.4209	$94.42	$94.40	$94.40
Purchase #5	$78.46	8.853%	$85.4061	$85.41	$85.40	$85.40
Purchase #6	$162.40	9.254%	$177.4285	$177.43	$177.45	$177.40
Purchase #7	$77.78	10.159%	$85.6817	$85.68	$85.70	$85.70
7 purchase totals =	$891.64		$962.2279	$962.23	$962.20	$962.20