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	$134.33	10.458%	$148.3782	$148.38	$148.40	$148.40
Purchase #2	$123.99	11.690%	$138.4844	$138.48	$138.50	$138.50
Purchase #3	$242.80	13.433%	$275.4153	$275.42	$275.40	$275.40
Purchase #4	$114.47	4.402%	$119.509	$119.51	$119.50	$119.50
Purchase #5	$240.65	13.351%	$272.7792	$272.78	$272.80	$272.80
Purchase #6	$193.61	12.561%	$217.9294	$217.93	$217.95	$217.90
Purchase #7	$89.54	12.202%	$100.4657	$100.47	$100.45	$100.50
7 purchase totals =	$1,139.39		$1,272.9612	$1,272.97	$1,273.00	$1,273.00