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	$246.31	3.627%	$255.2437	$255.24	$255.25	$255.20
Purchase #2	$216.89	3.671%	$224.852	$224.85	$224.85	$224.90
Purchase #3	$238.61	4.559%	$249.4882	$249.49	$249.50	$249.50
Purchase #4	$169.56	11.395%	$188.8814	$188.88	$188.90	$188.90
Purchase #5	$133.33	4.773%	$139.6938	$139.69	$139.70	$139.70
Purchase #6	$90.40	9.373%	$98.8732	$98.87	$98.85	$98.90
Purchase #7	$117.80	12.176%	$132.1433	$132.14	$132.15	$132.10
7 purchase totals =	$1,212.90		$1,289.1756	$1,289.16	$1,289.20	$1,289.20