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	$145.89	4.105%	$151.8788	$151.88	$151.90	$151.90
Purchase #2	$90.68	10.869%	$100.536	$100.54	$100.55	$100.50
Purchase #3	$139.90	12.658%	$157.6085	$157.61	$157.60	$157.60
Purchase #4	$206.96	12.817%	$233.4861	$233.49	$233.50	$233.50
Purchase #5	$124.59	12.369%	$140.0005	$140.00	$140.00	$140.00
Purchase #6	$69.81	10.450%	$77.1051	$77.11	$77.10	$77.10
Purchase #7	$51.83	5.147%	$54.4977	$54.50	$54.50	$54.50
7 purchase totals =	$829.66		$915.1127	$915.13	$915.15	$915.10