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	$66.67	12.241%	$74.8311	$74.83	$74.85	$74.80
Purchase #2	$132.78	13.296%	$150.4344	$150.43	$150.45	$150.40
Purchase #3	$118.80	11.825%	$132.8481	$132.85	$132.85	$132.80
Purchase #4	$172.98	5.444%	$182.397	$182.40	$182.40	$182.40
Purchase #5	$149.89	5.317%	$157.8597	$157.86	$157.85	$157.90
Purchase #6	$153.40	12.422%	$172.4553	$172.46	$172.45	$172.50
Purchase #7	$237.51	4.635%	$248.5186	$248.52	$248.50	$248.50
7 purchase totals =	$1,032.03		$1,119.3442	$1,119.35	$1,119.35	$1,119.30