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	$34.25	10.679%	$37.9076	$37.91	$37.90	$37.90
Purchase #2	$28.75	13.853%	$32.7327	$32.73	$32.75	$32.70
Purchase #3	$100.82	10.240%	$111.144	$111.14	$111.15	$111.10
Purchase #4	$246.49	9.513%	$269.9386	$269.94	$269.95	$269.90
Purchase #5	$187.45	9.391%	$205.0534	$205.05	$205.05	$205.10
Purchase #6	$121.47	8.744%	$132.0913	$132.09	$132.10	$132.10
Purchase #7	$242.93	4.732%	$254.4254	$254.43	$254.45	$254.40
7 purchase totals =	$962.16		$1,043.2930	$1,043.29	$1,043.35	$1,043.20