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	$157.37	9.532%	$172.3705	$172.37	$172.35	$172.40
Purchase #2	$59.49	4.788%	$62.3384	$62.34	$62.35	$62.30
Purchase #3	$93.78	10.412%	$103.5444	$103.54	$103.55	$103.50
Purchase #4	$16.53	10.514%	$18.268	$18.27	$18.25	$18.30
Purchase #5	$158.35	13.145%	$179.1651	$179.17	$179.15	$179.20
Purchase #6	$68.99	11.303%	$76.7879	$76.79	$76.80	$76.80
Purchase #7	$54.65	9.599%	$59.8959	$59.90	$59.90	$59.90
7 purchase totals =	$609.16		$672.3702	$672.38	$672.35	$672.40