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	$122.86	12.725%	$138.4939	$138.49	$138.50	$138.50
Purchase #2	$195.52	13.548%	$222.009	$222.01	$222.00	$222.00
Purchase #3	$221.97	4.128%	$231.1329	$231.13	$231.15	$231.10
Purchase #4	$26.97	7.834%	$29.0828	$29.08	$29.10	$29.10
Purchase #5	$160.51	12.489%	$180.5561	$180.56	$180.55	$180.60
Purchase #6	$134.43	11.664%	$150.1099	$150.11	$150.10	$150.10
Purchase #7	$155.85	13.254%	$176.5064	$176.51	$176.50	$176.50
7 purchase totals =	$1,018.11		$1,127.8910	$1,127.89	$1,127.90	$1,127.90