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	$28.77	13.784%	$32.7357	$32.74	$32.75	$32.70
Purchase #2	$102.89	8.457%	$111.5914	$111.59	$111.60	$111.60
Purchase #3	$62.97	7.161%	$67.4793	$67.48	$67.50	$67.50
Purchase #4	$225.98	4.208%	$235.4892	$235.49	$235.50	$235.50
Purchase #5	$93.66	11.671%	$104.5911	$104.59	$104.60	$104.60
Purchase #6	$164.50	11.547%	$183.4948	$183.49	$183.50	$183.50
Purchase #7	$39.98	5.812%	$42.3036	$42.30	$42.30	$42.30
7 purchase totals =	$718.75		$777.6851	$777.68	$777.75	$777.70