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	$119.87	3.414%	$123.9624	$123.96	$123.95	$124.00
Purchase #2	$197.26	12.850%	$222.6079	$222.61	$222.60	$222.60
Purchase #3	$164.77	13.233%	$186.574	$186.57	$186.55	$186.60
Purchase #4	$141.60	11.619%	$158.0525	$158.05	$158.05	$158.10
Purchase #5	$223.81	10.745%	$247.8584	$247.86	$247.85	$247.90
Purchase #6	$233.60	4.729%	$244.6469	$244.65	$244.65	$244.60
Purchase #7	$95.25	5.392%	$100.3859	$100.39	$100.40	$100.40
7 purchase totals =	$1,176.16		$1,284.0880	$1,284.09	$1,284.05	$1,284.20