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	$33.84	13.739%	$38.4893	$38.49	$38.50	$38.50
Purchase #2	$14.89	7.362%	$15.9862	$15.99	$16.00	$16.00
Purchase #3	$41.38	9.326%	$45.2391	$45.24	$45.25	$45.20
Purchase #4	$85.28	6.383%	$90.7234	$90.72	$90.70	$90.70
Purchase #5	$219.55	12.199%	$246.3329	$246.33	$246.35	$246.30
Purchase #6	$230.90	13.857%	$262.8958	$262.90	$262.90	$262.90
Purchase #7	$237.30	3.496%	$245.596	$245.60	$245.60	$245.60
7 purchase totals =	$863.14		$945.2627	$945.27	$945.30	$945.20