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	$62.58	13.242%	$70.8668	$70.87	$70.85	$70.90
Purchase #2	$245.56	11.239%	$273.1585	$273.16	$273.15	$273.20
Purchase #3	$147.89	13.160%	$167.3523	$167.35	$167.35	$167.40
Purchase #4	$144.94	13.471%	$164.4649	$164.46	$164.45	$164.50
Purchase #5	$131.45	7.335%	$141.0919	$141.09	$141.10	$141.10
Purchase #6	$21.93	6.832%	$23.4283	$23.43	$23.45	$23.40
Purchase #7	$106.25	4.474%	$111.0036	$111.00	$111.00	$111.00
7 purchase totals =	$860.60		$951.3663	$951.36	$951.35	$951.50