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	$95.62	5.435%	$100.8169	$100.82	$100.80	$100.80
Purchase #2	$249.88	9.871%	$274.5457	$274.55	$274.55	$274.50
Purchase #3	$157.27	5.634%	$166.1306	$166.13	$166.15	$166.10
Purchase #4	$119.29	9.336%	$130.4269	$130.43	$130.45	$130.40
Purchase #5	$211.57	4.325%	$220.7204	$220.72	$220.70	$220.70
Purchase #6	$239.58	13.600%	$272.1629	$272.16	$272.15	$272.20
Purchase #7	$96.61	10.528%	$106.7811	$106.78	$106.80	$106.80
7 purchase totals =	$1,169.82		$1,271.5845	$1,271.59	$1,271.60	$1,271.50