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	$13.72	12.763%	$15.4711	$15.47	$15.45	$15.50
Purchase #2	$173.44	11.496%	$193.3787	$193.38	$193.40	$193.40
Purchase #3	$49.98	7.383%	$53.67	$53.67	$53.65	$53.70
Purchase #4	$81.93	10.350%	$90.4098	$90.41	$90.40	$90.40
Purchase #5	$30.29	4.124%	$31.5392	$31.54	$31.55	$31.50
Purchase #6	$111.43	8.141%	$120.5015	$120.50	$120.50	$120.50
Purchase #7	$104.64	4.126%	$108.9574	$108.96	$108.95	$109.00
7 purchase totals =	$565.43		$613.9277	$613.93	$613.90	$614.00