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	$138.88	13.472%	$157.5899	$157.59	$157.60	$157.60
Purchase #2	$99.75	4.525%	$104.2637	$104.26	$104.25	$104.30
Purchase #3	$240.45	8.113%	$259.9577	$259.96	$259.95	$260.00
Purchase #4	$18.54	5.650%	$19.5875	$19.59	$19.60	$19.60
Purchase #5	$122.81	4.490%	$128.3242	$128.32	$128.30	$128.30
Purchase #6	$215.96	12.667%	$243.3157	$243.32	$243.30	$243.30
Purchase #7	$134.57	13.755%	$153.0801	$153.08	$153.10	$153.10
7 purchase totals =	$970.96		$1,066.1188	$1,066.12	$1,066.10	$1,066.20