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	$100.67	4.215%	$104.9132	$104.91	$104.90	$104.90
Purchase #2	$159.83	3.838%	$165.9643	$165.96	$165.95	$166.00
Purchase #3	$152.96	12.509%	$172.0938	$172.09	$172.10	$172.10
Purchase #4	$146.93	12.470%	$165.2522	$165.25	$165.25	$165.30
Purchase #5	$244.65	12.774%	$275.9016	$275.90	$275.90	$275.90
Purchase #6	$170.67	3.568%	$176.7595	$176.76	$176.75	$176.80
Purchase #7	$136.38	13.599%	$154.9263	$154.93	$154.95	$154.90
7 purchase totals =	$1,112.09		$1,215.8109	$1,215.80	$1,215.80	$1,215.90