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	$248.64	12.452%	$279.6007	$279.60	$279.60	$279.60
Purchase #2	$246.89	13.217%	$279.5215	$279.52	$279.50	$279.50
Purchase #3	$126.49	9.467%	$138.4648	$138.46	$138.45	$138.50
Purchase #4	$210.56	3.602%	$218.1444	$218.14	$218.15	$218.10
Purchase #5	$145.40	3.656%	$150.7158	$150.72	$150.70	$150.70
Purchase #6	$137.89	10.632%	$152.5505	$152.55	$152.55	$152.60
Purchase #7	$207.67	6.487%	$221.1416	$221.14	$221.15	$221.10
7 purchase totals =	$1,323.54		$1,440.1393	$1,440.13	$1,440.10	$1,440.10