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	$119.60	12.105%	$134.0776	$134.08	$134.10	$134.10
Purchase #2	$15.69	7.259%	$16.8289	$16.83	$16.85	$16.80
Purchase #3	$51.62	3.496%	$53.4246	$53.42	$53.40	$53.40
Purchase #4	$243.52	13.145%	$275.5307	$275.53	$275.55	$275.50
Purchase #5	$139.57	8.218%	$151.0399	$151.04	$151.05	$151.00
Purchase #6	$102.94	5.255%	$108.3495	$108.35	$108.35	$108.30
Purchase #7	$55.58	10.786%	$61.5749	$61.57	$61.55	$61.60
7 purchase totals =	$728.52		$800.8261	$800.82	$800.85	$800.70