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	$91.87	8.711%	$99.8728	$99.87	$99.85	$99.90
Purchase #2	$234.89	13.472%	$266.5344	$266.53	$266.55	$266.50
Purchase #3	$143.31	6.758%	$152.9949	$152.99	$153.00	$153.00
Purchase #4	$48.85	11.316%	$54.3779	$54.38	$54.40	$54.40
Purchase #5	$87.30	7.194%	$93.5804	$93.58	$93.60	$93.60
Purchase #6	$149.52	3.723%	$155.0866	$155.09	$155.10	$155.10
Purchase #7	$37.97	10.345%	$41.898	$41.90	$41.90	$41.90
7 purchase totals =	$793.71		$864.3450	$864.34	$864.40	$864.40