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	$12.84	4.177%	$13.3763	$13.38	$13.40	$13.40
Purchase #2	$6.40	7.221%	$6.8621	$6.86	$6.85	$6.90
Purchase #3	$24.82	12.854%	$28.0104	$28.01	$28.00	$28.00
Purchase #4	$210.82	9.857%	$231.6005	$231.60	$231.60	$231.60
Purchase #5	$78.84	13.836%	$89.7483	$89.75	$89.75	$89.70
Purchase #6	$205.58	6.271%	$218.4719	$218.47	$218.45	$218.50
Purchase #7	$83.40	8.346%	$90.3606	$90.36	$90.35	$90.40
7 purchase totals =	$622.70		$678.4301	$678.43	$678.40	$678.50