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	$128.49	12.672%	$144.7723	$144.77	$144.75	$144.80
Purchase #2	$212.66	7.440%	$228.4819	$228.48	$228.50	$228.50
Purchase #3	$192.69	9.733%	$211.4445	$211.44	$211.45	$211.40
Purchase #4	$172.84	11.514%	$192.7408	$192.74	$192.75	$192.70
Purchase #5	$191.93	13.466%	$217.7753	$217.78	$217.80	$217.80
Purchase #6	$80.49	10.735%	$89.1306	$89.13	$89.15	$89.10
Purchase #7	$73.34	13.827%	$83.4807	$83.48	$83.50	$83.50
7 purchase totals =	$1,052.44		$1,167.8261	$1,167.82	$1,167.90	$1,167.80