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	$243.88	5.221%	$256.613	$256.61	$256.60	$256.60
Purchase #2	$10.73	10.693%	$11.8774	$11.88	$11.90	$11.90
Purchase #3	$183.91	13.277%	$208.3277	$208.33	$208.35	$208.30
Purchase #4	$33.31	6.612%	$35.5125	$35.51	$35.50	$35.50
Purchase #5	$15.51	13.728%	$17.6392	$17.64	$17.65	$17.60
Purchase #6	$34.95	13.236%	$39.576	$39.58	$39.60	$39.60
Purchase #7	$85.55	7.340%	$91.8294	$91.83	$91.85	$91.80
7 purchase totals =	$607.84		$661.3752	$661.38	$661.45	$661.30