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	$105.69	13.345%	$119.7943	$119.79	$119.80	$119.80
Purchase #2	$61.74	8.251%	$66.8342	$66.83	$66.85	$66.80
Purchase #3	$32.46	13.281%	$36.771	$36.77	$36.75	$36.80
Purchase #4	$25.66	13.842%	$29.2119	$29.21	$29.20	$29.20
Purchase #5	$109.96	4.417%	$114.8169	$114.82	$114.80	$114.80
Purchase #6	$34.34	9.320%	$37.5405	$37.54	$37.55	$37.50
Purchase #7	$95.71	9.329%	$104.6388	$104.64	$104.65	$104.60
7 purchase totals =	$465.56		$509.6076	$509.60	$509.60	$509.50