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	$131.81	11.245%	$146.632	$146.63	$146.65	$146.60
Purchase #2	$46.80	6.584%	$49.8813	$49.88	$49.90	$49.90
Purchase #3	$183.91	3.603%	$190.5363	$190.54	$190.55	$190.50
Purchase #4	$138.92	3.845%	$144.2615	$144.26	$144.25	$144.30
Purchase #5	$44.31	13.369%	$50.2338	$50.23	$50.25	$50.20
Purchase #6	$44.81	8.654%	$48.6879	$48.69	$48.70	$48.70
Purchase #7	$95.38	4.373%	$99.551	$99.55	$99.55	$99.60
7 purchase totals =	$685.94		$729.7838	$729.78	$729.85	$729.80