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	$45.80	7.597%	$49.2794	$49.28	$49.30	$49.30
Purchase #2	$78.55	13.461%	$89.1236	$89.12	$89.10	$89.10
Purchase #3	$61.87	10.867%	$68.5934	$68.59	$68.60	$68.60
Purchase #4	$108.33	13.659%	$123.1268	$123.13	$123.15	$123.10
Purchase #5	$100.35	10.860%	$111.248	$111.25	$111.25	$111.20
Purchase #6	$95.52	13.434%	$108.3522	$108.35	$108.35	$108.40
Purchase #7	$225.81	12.561%	$254.174	$254.17	$254.15	$254.20
7 purchase totals =	$716.23		$803.8974	$803.89	$803.90	$803.90