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	$129.59	9.368%	$141.73	$141.73	$141.75	$141.70
Purchase #2	$127.83	3.704%	$132.5648	$132.56	$132.55	$132.60
Purchase #3	$29.71	8.543%	$32.2481	$32.25	$32.25	$32.20
Purchase #4	$53.59	12.358%	$60.2127	$60.21	$60.20	$60.20
Purchase #5	$20.38	7.145%	$21.8362	$21.84	$21.85	$21.80
Purchase #6	$46.51	13.208%	$52.653	$52.65	$52.65	$52.70
Purchase #7	$228.82	4.407%	$238.9041	$238.90	$238.90	$238.90
7 purchase totals =	$636.43		$680.1489	$680.14	$680.15	$680.10