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	$250.58	6.321%	$266.4192	$266.42	$266.40	$266.40
Purchase #2	$12.46	11.567%	$13.9012	$13.90	$13.90	$13.90
Purchase #3	$50.42	11.814%	$56.3766	$56.38	$56.40	$56.40
Purchase #4	$50.76	8.735%	$55.1939	$55.19	$55.20	$55.20
Purchase #5	$154.29	12.285%	$173.2445	$173.24	$173.25	$173.20
Purchase #6	$16.75	12.757%	$18.8868	$18.89	$18.90	$18.90
Purchase #7	$121.78	5.373%	$128.3232	$128.32	$128.30	$128.30
7 purchase totals =	$657.04		$712.3454	$712.34	$712.35	$712.30