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	$132.36	10.220%	$145.8872	$145.89	$145.90	$145.90
Purchase #2	$32.35	6.513%	$34.457	$34.46	$34.45	$34.50
Purchase #3	$116.90	9.252%	$127.7156	$127.72	$127.70	$127.70
Purchase #4	$189.84	4.345%	$198.0885	$198.09	$198.10	$198.10
Purchase #5	$93.71	5.730%	$99.0796	$99.08	$99.10	$99.10
Purchase #6	$129.41	10.524%	$143.0291	$143.03	$143.05	$143.00
Purchase #7	$61.90	7.544%	$66.5697	$66.57	$66.55	$66.60
7 purchase totals =	$756.47		$814.8267	$814.84	$814.85	$814.90