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	$243.72	12.774%	$274.8528	$274.85	$274.85	$274.90
Purchase #2	$76.40	8.338%	$82.7702	$82.77	$82.75	$82.80
Purchase #3	$70.72	12.843%	$79.8026	$79.80	$79.80	$79.80
Purchase #4	$230.81	7.788%	$248.7855	$248.79	$248.80	$248.80
Purchase #5	$104.87	5.873%	$111.029	$111.03	$111.05	$111.00
Purchase #6	$132.94	13.833%	$151.3296	$151.33	$151.35	$151.30
Purchase #7	$122.83	7.109%	$131.562	$131.56	$131.55	$131.60
7 purchase totals =	$982.29		$1,080.1317	$1,080.13	$1,080.15	$1,080.20