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	$231.56	3.863%	$240.5052	$240.51	$240.50	$240.50
Purchase #2	$15.79	3.324%	$16.3149	$16.31	$16.30	$16.30
Purchase #3	$186.35	9.458%	$203.975	$203.98	$204.00	$204.00
Purchase #4	$70.66	10.409%	$78.015	$78.02	$78.00	$78.00
Purchase #5	$158.61	6.649%	$169.156	$169.16	$169.15	$169.20
Purchase #6	$234.41	13.443%	$265.9217	$265.92	$265.90	$265.90
Purchase #7	$53.97	10.403%	$59.5845	$59.58	$59.60	$59.60
7 purchase totals =	$951.35		$1,033.4723	$1,033.48	$1,033.45	$1,033.50