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	$183.55	4.550%	$191.9015	$191.90	$191.90	$191.90
Purchase #2	$212.63	8.862%	$231.4733	$231.47	$231.45	$231.50
Purchase #3	$28.54	10.451%	$31.5227	$31.52	$31.50	$31.50
Purchase #4	$87.78	12.667%	$98.8991	$98.90	$98.90	$98.90
Purchase #5	$145.42	9.166%	$158.7492	$158.75	$158.75	$158.70
Purchase #6	$24.55	11.288%	$27.3212	$27.32	$27.30	$27.30
Purchase #7	$44.60	10.560%	$49.3098	$49.31	$49.30	$49.30
7 purchase totals =	$727.07		$789.1768	$789.17	$789.10	$789.10