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	$164.96	11.338%	$183.6632	$183.66	$183.65	$183.70
Purchase #2	$113.54	4.389%	$118.5233	$118.52	$118.50	$118.50
Purchase #3	$42.83	6.243%	$45.5039	$45.50	$45.50	$45.50
Purchase #4	$226.75	12.676%	$255.4928	$255.49	$255.50	$255.50
Purchase #5	$138.29	8.625%	$150.2175	$150.22	$150.20	$150.20
Purchase #6	$74.71	5.200%	$78.5949	$78.59	$78.60	$78.60
Purchase #7	$138.53	3.822%	$143.8246	$143.82	$143.80	$143.80
7 purchase totals =	$899.61		$975.8202	$975.80	$975.75	$975.80