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	$231.42	12.229%	$259.7204	$259.72	$259.70	$259.70
Purchase #2	$36.42	10.413%	$40.2124	$40.21	$40.20	$40.20
Purchase #3	$205.55	8.436%	$222.8902	$222.89	$222.90	$222.90
Purchase #4	$184.32	13.547%	$209.2898	$209.29	$209.30	$209.30
Purchase #5	$29.82	11.533%	$33.2591	$33.26	$33.25	$33.30
Purchase #6	$124.52	4.505%	$130.1296	$130.13	$130.15	$130.10
Purchase #7	$224.89	7.137%	$240.9404	$240.94	$240.95	$240.90
7 purchase totals =	$1,036.94		$1,136.4419	$1,136.44	$1,136.45	$1,136.40