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	$77.56	4.657%	$81.172	$81.17	$81.15	$81.20
Purchase #2	$45.68	8.535%	$49.5788	$49.58	$49.60	$49.60
Purchase #3	$114.31	7.641%	$123.0444	$123.04	$123.05	$123.00
Purchase #4	$176.49	13.813%	$200.8686	$200.87	$200.85	$200.90
Purchase #5	$212.83	13.341%	$241.2237	$241.22	$241.20	$241.20
Purchase #6	$153.32	5.612%	$161.9243	$161.92	$161.90	$161.90
Purchase #7	$35.39	5.731%	$37.4182	$37.42	$37.40	$37.40
7 purchase totals =	$815.58		$895.2300	$895.22	$895.15	$895.20