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	$160.48	12.756%	$180.9508	$180.95	$180.95	$181.00
Purchase #2	$126.25	3.471%	$130.6321	$130.63	$130.65	$130.60
Purchase #3	$242.76	5.326%	$255.6894	$255.69	$255.70	$255.70
Purchase #4	$66.59	9.395%	$72.8461	$72.85	$72.85	$72.80
Purchase #5	$46.87	7.621%	$50.442	$50.44	$50.45	$50.40
Purchase #6	$175.86	8.765%	$191.2741	$191.27	$191.25	$191.30
Purchase #7	$105.67	10.463%	$116.7263	$116.73	$116.75	$116.70
7 purchase totals =	$924.48		$998.5608	$998.56	$998.60	$998.50