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	$41.45	7.313%	$44.4812	$44.48	$44.50	$44.50
Purchase #2	$139.58	10.192%	$153.806	$153.81	$153.80	$153.80
Purchase #3	$244.86	11.146%	$272.1521	$272.15	$272.15	$272.20
Purchase #4	$158.85	5.710%	$167.9203	$167.92	$167.90	$167.90
Purchase #5	$58.97	12.729%	$66.4763	$66.48	$66.50	$66.50
Purchase #6	$115.33	13.231%	$130.5893	$130.59	$130.60	$130.60
Purchase #7	$32.38	9.501%	$35.4564	$35.46	$35.45	$35.50
7 purchase totals =	$791.42		$870.8816	$870.89	$870.90	$871.00