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	$32.37	3.381%	$33.4644	$33.46	$33.45	$33.50
Purchase #2	$69.31	13.420%	$78.6114	$78.61	$78.60	$78.60
Purchase #3	$214.30	10.490%	$236.7801	$236.78	$236.80	$236.80
Purchase #4	$67.84	6.382%	$72.1695	$72.17	$72.15	$72.20
Purchase #5	$204.34	4.374%	$213.2778	$213.28	$213.30	$213.30
Purchase #6	$132.69	10.558%	$146.6994	$146.70	$146.70	$146.70
Purchase #7	$26.98	8.117%	$29.17	$29.17	$29.15	$29.20
7 purchase totals =	$747.83		$810.1726	$810.17	$810.15	$810.30