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	$105.60	11.357%	$117.593	$117.59	$117.60	$117.60
Purchase #2	$135.58	6.111%	$143.8653	$143.87	$143.85	$143.90
Purchase #3	$65.51	4.562%	$68.4986	$68.50	$68.50	$68.50
Purchase #4	$201.78	10.232%	$222.4261	$222.43	$222.45	$222.40
Purchase #5	$246.95	11.634%	$275.6802	$275.68	$275.70	$275.70
Purchase #6	$27.76	12.544%	$31.2422	$31.24	$31.25	$31.20
Purchase #7	$206.70	7.556%	$222.3183	$222.32	$222.30	$222.30
7 purchase totals =	$989.88		$1,081.6237	$1,081.63	$1,081.65	$1,081.60