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	$63.27	4.628%	$66.1981	$66.20	$66.20	$66.20
Purchase #2	$122.79	13.594%	$139.4821	$139.48	$139.50	$139.50
Purchase #3	$59.79	10.658%	$66.1624	$66.16	$66.15	$66.20
Purchase #4	$49.37	10.116%	$54.3643	$54.36	$54.35	$54.40
Purchase #5	$92.87	11.179%	$103.2519	$103.25	$103.25	$103.30
Purchase #6	$150.97	9.803%	$165.7696	$165.77	$165.75	$165.80
Purchase #7	$44.66	12.421%	$50.2072	$50.21	$50.20	$50.20
7 purchase totals =	$583.72		$645.4356	$645.43	$645.40	$645.60