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	$128.64	6.637%	$137.1778	$137.18	$137.20	$137.20
Purchase #2	$98.63	12.545%	$111.0031	$111.00	$111.00	$111.00
Purchase #3	$204.28	13.161%	$231.1653	$231.17	$231.15	$231.20
Purchase #4	$166.77	13.597%	$189.4457	$189.45	$189.45	$189.40
Purchase #5	$11.88	11.863%	$13.2893	$13.29	$13.30	$13.30
Purchase #6	$107.61	5.803%	$113.8546	$113.85	$113.85	$113.90
Purchase #7	$91.59	12.719%	$103.2393	$103.24	$103.25	$103.20
7 purchase totals =	$809.40		$899.1751	$899.18	$899.20	$899.20