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	$201.56	11.575%	$224.8906	$224.89	$224.90	$224.90
Purchase #2	$69.86	11.856%	$78.1426	$78.14	$78.15	$78.10
Purchase #3	$12.36	13.839%	$14.0705	$14.07	$14.05	$14.10
Purchase #4	$161.51	10.173%	$177.9404	$177.94	$177.95	$177.90
Purchase #5	$96.48	7.249%	$103.4738	$103.47	$103.45	$103.50
Purchase #6	$33.89	13.322%	$38.4048	$38.40	$38.40	$38.40
Purchase #7	$52.77	4.452%	$55.1193	$55.12	$55.10	$55.10
7 purchase totals =	$628.43		$692.0420	$692.03	$692.00	$692.00