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	$153.65	3.691%	$159.3212	$159.32	$159.30	$159.30
Purchase #2	$113.42	9.420%	$124.1042	$124.10	$124.10	$124.10
Purchase #3	$100.91	4.446%	$105.3965	$105.40	$105.40	$105.40
Purchase #4	$29.91	11.494%	$33.3479	$33.35	$33.35	$33.30
Purchase #5	$121.39	13.197%	$137.4098	$137.41	$137.40	$137.40
Purchase #6	$64.55	4.702%	$67.5851	$67.59	$67.60	$67.60
Purchase #7	$127.67	9.338%	$139.5918	$139.59	$139.60	$139.60
7 purchase totals =	$711.50		$766.7565	$766.76	$766.75	$766.70