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	$10.95	3.249%	$11.3058	$11.31	$11.30	$11.30
Purchase #2	$83.49	13.323%	$94.6134	$94.61	$94.60	$94.60
Purchase #3	$241.30	5.792%	$255.2761	$255.28	$255.30	$255.30
Purchase #4	$204.86	11.405%	$228.2243	$228.22	$228.20	$228.20
Purchase #5	$182.45	5.200%	$191.9374	$191.94	$191.95	$191.90
Purchase #6	$26.81	6.497%	$28.5518	$28.55	$28.55	$28.60
Purchase #7	$14.51	6.783%	$15.4942	$15.49	$15.50	$15.50
7 purchase totals =	$764.37		$825.4030	$825.40	$825.40	$825.40