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	$122.68	12.509%	$138.026	$138.03	$138.05	$138.00
Purchase #2	$235.50	6.766%	$251.4339	$251.43	$251.45	$251.40
Purchase #3	$222.51	3.131%	$229.4768	$229.48	$229.50	$229.50
Purchase #4	$235.81	3.253%	$243.4809	$243.48	$243.50	$243.50
Purchase #5	$148.76	11.223%	$165.4553	$165.46	$165.45	$165.50
Purchase #6	$126.88	4.198%	$132.2064	$132.21	$132.20	$132.20
Purchase #7	$106.98	4.510%	$111.8048	$111.80	$111.80	$111.80
7 purchase totals =	$1,199.12		$1,271.8841	$1,271.89	$1,271.95	$1,271.90