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	$91.45	13.348%	$103.6567	$103.66	$103.65	$103.70
Purchase #2	$132.95	4.245%	$138.5937	$138.59	$138.60	$138.60
Purchase #3	$98.55	8.806%	$107.2283	$107.23	$107.25	$107.20
Purchase #4	$72.80	7.572%	$78.3124	$78.31	$78.30	$78.30
Purchase #5	$176.54	4.773%	$184.9663	$184.97	$184.95	$185.00
Purchase #6	$117.83	12.421%	$132.4657	$132.47	$132.45	$132.50
Purchase #7	$38.55	12.272%	$43.2809	$43.28	$43.30	$43.30
7 purchase totals =	$728.67		$788.5040	$788.51	$788.50	$788.60