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	$78.25	12.177%	$87.7785	$87.78	$87.80	$87.80
Purchase #2	$140.83	7.776%	$151.7809	$151.78	$151.80	$151.80
Purchase #3	$81.60	10.639%	$90.2814	$90.28	$90.30	$90.30
Purchase #4	$153.49	12.607%	$172.8405	$172.84	$172.85	$172.80
Purchase #5	$117.63	11.815%	$131.528	$131.53	$131.55	$131.50
Purchase #6	$76.51	6.852%	$81.7525	$81.75	$81.75	$81.80
Purchase #7	$107.33	7.518%	$115.3991	$115.40	$115.40	$115.40
7 purchase totals =	$755.64		$831.3609	$831.36	$831.45	$831.40