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	$9.61	8.111%	$10.3895	$10.39	$10.40	$10.40
Purchase #2	$124.59	9.286%	$136.1594	$136.16	$136.15	$136.20
Purchase #3	$150.35	5.408%	$158.4809	$158.48	$158.50	$158.50
Purchase #4	$119.34	9.164%	$130.2763	$130.28	$130.30	$130.30
Purchase #5	$139.74	10.484%	$154.3903	$154.39	$154.40	$154.40
Purchase #6	$224.43	3.760%	$232.8686	$232.87	$232.85	$232.90
Purchase #7	$227.37	13.705%	$258.5311	$258.53	$258.55	$258.50
7 purchase totals =	$995.43		$1,081.0961	$1,081.10	$1,081.15	$1,081.20