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	$41.70	13.718%	$47.4204	$47.42	$47.40	$47.40
Purchase #2	$30.81	6.588%	$32.8398	$32.84	$32.85	$32.80
Purchase #3	$157.61	7.266%	$169.0619	$169.06	$169.05	$169.10
Purchase #4	$100.74	10.520%	$111.3378	$111.34	$111.35	$111.30
Purchase #5	$76.89	3.350%	$79.4658	$79.47	$79.45	$79.50
Purchase #6	$72.30	8.490%	$78.4383	$78.44	$78.45	$78.40
Purchase #7	$98.77	12.866%	$111.4777	$111.48	$111.50	$111.50
7 purchase totals =	$578.82		$630.0417	$630.05	$630.05	$630.00