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	$200.52	11.173%	$222.9241	$222.92	$222.90	$222.90
Purchase #2	$55.69	6.615%	$59.3739	$59.37	$59.35	$59.40
Purchase #3	$230.91	13.827%	$262.8379	$262.84	$262.85	$262.80
Purchase #4	$241.67	7.318%	$259.3554	$259.36	$259.35	$259.40
Purchase #5	$184.89	4.601%	$193.3968	$193.40	$193.40	$193.40
Purchase #6	$248.33	12.666%	$279.7835	$279.78	$279.80	$279.80
Purchase #7	$66.61	10.521%	$73.618	$73.62	$73.60	$73.60
7 purchase totals =	$1,228.62		$1,351.2896	$1,351.29	$1,351.25	$1,351.30