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	$92.27	7.198%	$98.9116	$98.91	$98.90	$98.90
Purchase #2	$34.50	11.141%	$38.3436	$38.34	$38.35	$38.30
Purchase #3	$119.26	4.748%	$124.9225	$124.92	$124.90	$124.90
Purchase #4	$51.85	12.473%	$58.3173	$58.32	$58.30	$58.30
Purchase #5	$196.71	13.360%	$222.9905	$222.99	$223.00	$223.00
Purchase #6	$45.91	10.249%	$50.6153	$50.62	$50.60	$50.60
Purchase #7	$48.89	6.126%	$51.885	$51.89	$51.90	$51.90
7 purchase totals =	$589.39		$645.9858	$645.99	$645.95	$645.90