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	$124.63	6.375%	$132.5752	$132.58	$132.60	$132.60
Purchase #2	$140.49	7.417%	$150.9101	$150.91	$150.90	$150.90
Purchase #3	$94.40	10.105%	$103.9391	$103.94	$103.95	$103.90
Purchase #4	$138.77	5.374%	$146.2275	$146.23	$146.25	$146.20
Purchase #5	$91.30	8.376%	$98.9473	$98.95	$98.95	$98.90
Purchase #6	$116.85	9.119%	$127.5056	$127.51	$127.50	$127.50
Purchase #7	$44.99	3.610%	$46.6141	$46.61	$46.60	$46.60
7 purchase totals =	$751.43		$806.7189	$806.73	$806.75	$806.60