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	$217.91	6.103%	$231.209	$231.21	$231.20	$231.20
Purchase #2	$72.93	11.526%	$81.3359	$81.34	$81.35	$81.30
Purchase #3	$156.50	8.604%	$169.9653	$169.97	$169.95	$170.00
Purchase #4	$64.52	3.141%	$66.5466	$66.55	$66.55	$66.50
Purchase #5	$147.27	11.776%	$164.6125	$164.61	$164.60	$164.60
Purchase #6	$79.95	13.105%	$90.4274	$90.43	$90.45	$90.40
Purchase #7	$115.41	13.436%	$130.9165	$130.92	$130.90	$130.90
7 purchase totals =	$854.49		$935.0132	$935.03	$935.00	$934.90