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	$64.34	3.535%	$66.6144	$66.61	$66.60	$66.60
Purchase #2	$19.37	5.674%	$20.4691	$20.47	$20.45	$20.50
Purchase #3	$133.92	9.518%	$146.6665	$146.67	$146.65	$146.70
Purchase #4	$34.58	10.220%	$38.1141	$38.11	$38.10	$38.10
Purchase #5	$33.93	10.420%	$37.4655	$37.47	$37.45	$37.50
Purchase #6	$150.41	11.157%	$167.1912	$167.19	$167.20	$167.20
Purchase #7	$135.28	13.220%	$153.164	$153.16	$153.15	$153.20
7 purchase totals =	$571.83		$629.6848	$629.68	$629.60	$629.80