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	$227.68	6.518%	$242.5202	$242.52	$242.50	$242.50
Purchase #2	$128.37	11.727%	$143.4239	$143.42	$143.40	$143.40
Purchase #3	$103.47	7.736%	$111.4744	$111.47	$111.45	$111.50
Purchase #4	$6.43	10.209%	$7.0864	$7.09	$7.10	$7.10
Purchase #5	$175.60	10.600%	$194.2136	$194.21	$194.20	$194.20
Purchase #6	$248.66	9.423%	$272.0912	$272.09	$272.10	$272.10
Purchase #7	$171.29	11.387%	$190.7948	$190.79	$190.80	$190.80
7 purchase totals =	$1,061.50		$1,161.6045	$1,161.59	$1,161.55	$1,161.60