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	$35.52	8.694%	$38.6081	$38.61	$38.60	$38.60
Purchase #2	$208.37	7.764%	$224.5478	$224.55	$224.55	$224.50
Purchase #3	$41.84	4.433%	$43.6948	$43.69	$43.70	$43.70
Purchase #4	$146.75	12.270%	$164.7562	$164.76	$164.75	$164.80
Purchase #5	$88.80	13.464%	$100.756	$100.76	$100.75	$100.80
Purchase #6	$240.55	8.726%	$261.5404	$261.54	$261.55	$261.50
Purchase #7	$193.69	6.147%	$205.5961	$205.60	$205.60	$205.60
7 purchase totals =	$955.52		$1,039.4994	$1,039.51	$1,039.50	$1,039.50