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	$124.68	6.364%	$132.6146	$132.61	$132.60	$132.60
Purchase #2	$62.69	12.340%	$70.4259	$70.43	$70.45	$70.40
Purchase #3	$93.66	7.588%	$100.7669	$100.77	$100.75	$100.80
Purchase #4	$98.40	4.484%	$102.8123	$102.81	$102.80	$102.80
Purchase #5	$33.36	12.660%	$37.5834	$37.58	$37.60	$37.60
Purchase #6	$65.57	5.663%	$69.2832	$69.28	$69.30	$69.30
Purchase #7	$92.35	8.789%	$100.4666	$100.47	$100.45	$100.50
7 purchase totals =	$570.71		$613.9529	$613.95	$613.95	$614.00