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	$85.78	9.353%	$93.803	$93.80	$93.80	$93.80
Purchase #2	$219.97	13.326%	$249.2832	$249.28	$249.30	$249.30
Purchase #3	$47.82	9.832%	$52.5217	$52.52	$52.50	$52.50
Purchase #4	$123.87	10.125%	$136.4118	$136.41	$136.40	$136.40
Purchase #5	$150.32	5.196%	$158.1306	$158.13	$158.15	$158.10
Purchase #6	$18.65	11.621%	$20.8173	$20.82	$20.80	$20.80
Purchase #7	$21.83	3.452%	$22.5836	$22.58	$22.60	$22.60
7 purchase totals =	$668.24		$733.5512	$733.54	$733.55	$733.50