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	$116.77	10.420%	$128.9374	$128.94	$128.95	$128.90
Purchase #2	$62.53	6.304%	$66.4719	$66.47	$66.45	$66.50
Purchase #3	$144.35	10.600%	$159.6511	$159.65	$159.65	$159.70
Purchase #4	$38.30	11.637%	$42.757	$42.76	$42.75	$42.80
Purchase #5	$83.65	12.722%	$94.292	$94.29	$94.30	$94.30
Purchase #6	$95.74	5.326%	$100.8391	$100.84	$100.85	$100.80
Purchase #7	$226.99	10.716%	$251.3142	$251.31	$251.30	$251.30
7 purchase totals =	$768.33		$844.2627	$844.26	$844.25	$844.30