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	$80.49	10.613%	$89.0324	$89.03	$89.05	$89.00
Purchase #2	$164.40	11.868%	$183.911	$183.91	$183.90	$183.90
Purchase #3	$181.80	6.665%	$193.917	$193.92	$193.90	$193.90
Purchase #4	$124.83	6.205%	$132.5757	$132.58	$132.60	$132.60
Purchase #5	$237.97	5.226%	$250.4063	$250.41	$250.40	$250.40
Purchase #6	$90.96	12.613%	$102.4328	$102.43	$102.45	$102.40
Purchase #7	$172.61	13.604%	$196.0919	$196.09	$196.10	$196.10
7 purchase totals =	$1,053.06		$1,148.3671	$1,148.37	$1,148.40	$1,148.30