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	$40.32	13.619%	$45.8112	$45.81	$45.80	$45.80
Purchase #2	$11.77	10.441%	$12.9989	$13.00	$13.00	$13.00
Purchase #3	$219.43	10.444%	$242.3473	$242.35	$242.35	$242.30
Purchase #4	$136.50	8.871%	$148.6089	$148.61	$148.60	$148.60
Purchase #5	$160.40	7.182%	$171.9199	$171.92	$171.90	$171.90
Purchase #6	$48.28	6.669%	$51.4998	$51.50	$51.50	$51.50
Purchase #7	$232.75	10.237%	$256.5766	$256.58	$256.60	$256.60
7 purchase totals =	$849.45		$929.7626	$929.77	$929.75	$929.70