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	$146.25	9.321%	$159.882	$159.88	$159.90	$159.90
Purchase #2	$203.43	5.520%	$214.6593	$214.66	$214.65	$214.70
Purchase #3	$16.74	6.304%	$17.7953	$17.80	$17.80	$17.80
Purchase #4	$112.42	8.778%	$122.2882	$122.29	$122.30	$122.30
Purchase #5	$100.98	10.435%	$111.5173	$111.52	$111.50	$111.50
Purchase #6	$190.61	3.277%	$196.8563	$196.86	$196.85	$196.90
Purchase #7	$103.61	12.385%	$116.4421	$116.44	$116.45	$116.40
7 purchase totals =	$874.04		$939.4405	$939.45	$939.45	$939.50