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	$34.99	6.792%	$37.3665	$37.37	$37.35	$37.40
Purchase #2	$41.59	9.435%	$45.514	$45.51	$45.50	$45.50
Purchase #3	$56.45	13.723%	$64.1966	$64.20	$64.20	$64.20
Purchase #4	$196.31	9.246%	$214.4608	$214.46	$214.45	$214.50
Purchase #5	$199.77	12.853%	$225.4464	$225.45	$225.45	$225.40
Purchase #6	$105.98	12.809%	$119.555	$119.56	$119.55	$119.60
Purchase #7	$86.60	13.160%	$97.9966	$98.00	$98.00	$98.00
7 purchase totals =	$721.69		$804.5359	$804.55	$804.50	$804.60