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	$146.32	4.489%	$152.8883	$152.89	$152.90	$152.90
Purchase #2	$60.90	10.866%	$67.5174	$67.52	$67.50	$67.50
Purchase #3	$233.64	11.872%	$261.3777	$261.38	$261.40	$261.40
Purchase #4	$38.87	12.453%	$43.7105	$43.71	$43.70	$43.70
Purchase #5	$144.54	9.374%	$158.0892	$158.09	$158.10	$158.10
Purchase #6	$208.83	9.228%	$228.1008	$228.10	$228.10	$228.10
Purchase #7	$9.90	5.771%	$10.4713	$10.47	$10.45	$10.50
7 purchase totals =	$843.00		$922.1552	$922.16	$922.15	$922.20