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	$54.74	8.104%	$59.1761	$59.18	$59.20	$59.20
Purchase #2	$202.30	10.871%	$224.292	$224.29	$224.30	$224.30
Purchase #3	$87.38	5.820%	$92.4655	$92.47	$92.45	$92.50
Purchase #4	$18.25	3.797%	$18.943	$18.94	$18.95	$18.90
Purchase #5	$70.81	13.853%	$80.6193	$80.62	$80.60	$80.60
Purchase #6	$228.95	10.792%	$253.6583	$253.66	$253.65	$253.70
Purchase #7	$35.48	9.571%	$38.8758	$38.88	$38.90	$38.90
7 purchase totals =	$697.91		$768.0300	$768.04	$768.05	$768.10