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	$208.69	6.797%	$222.8747	$222.87	$222.85	$222.90
Purchase #2	$132.58	9.296%	$144.9046	$144.90	$144.90	$144.90
Purchase #3	$55.40	13.457%	$62.8552	$62.86	$62.85	$62.90
Purchase #4	$175.25	8.177%	$189.5802	$189.58	$189.60	$189.60
Purchase #5	$33.80	11.132%	$37.5626	$37.56	$37.55	$37.60
Purchase #6	$106.81	12.194%	$119.8344	$119.83	$119.85	$119.80
Purchase #7	$27.42	9.595%	$30.0509	$30.05	$30.05	$30.10
7 purchase totals =	$739.95		$807.6626	$807.65	$807.65	$807.80