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	$29.81	11.855%	$33.344	$33.34	$33.35	$33.30
Purchase #2	$119.53	6.475%	$127.2696	$127.27	$127.25	$127.30
Purchase #3	$166.40	5.344%	$175.2924	$175.29	$175.30	$175.30
Purchase #4	$19.33	11.839%	$21.6185	$21.62	$21.60	$21.60
Purchase #5	$143.26	11.144%	$159.2249	$159.22	$159.20	$159.20
Purchase #6	$24.49	12.792%	$27.6228	$27.62	$27.60	$27.60
Purchase #7	$187.68	3.419%	$194.0968	$194.10	$194.10	$194.10
7 purchase totals =	$690.50		$738.4690	$738.46	$738.40	$738.40