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	$40.88	7.128%	$43.7939	$43.79	$43.80	$43.80
Purchase #2	$57.61	5.404%	$60.7232	$60.72	$60.70	$60.70
Purchase #3	$206.55	4.190%	$215.2044	$215.20	$215.20	$215.20
Purchase #4	$100.72	7.716%	$108.4916	$108.49	$108.50	$108.50
Purchase #5	$37.51	13.651%	$42.6305	$42.63	$42.65	$42.60
Purchase #6	$66.44	8.640%	$72.1804	$72.18	$72.20	$72.20
Purchase #7	$111.79	10.279%	$123.2809	$123.28	$123.30	$123.30
7 purchase totals =	$621.50		$666.3049	$666.29	$666.35	$666.30