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	$96.59	3.138%	$99.621	$99.62	$99.60	$99.60
Purchase #2	$201.67	9.209%	$220.2418	$220.24	$220.25	$220.20
Purchase #3	$56.71	5.185%	$59.6504	$59.65	$59.65	$59.70
Purchase #4	$248.54	5.509%	$262.2321	$262.23	$262.25	$262.20
Purchase #5	$119.51	12.734%	$134.7284	$134.73	$134.75	$134.70
Purchase #6	$130.39	4.645%	$136.4466	$136.45	$136.45	$136.40
Purchase #7	$210.30	9.659%	$230.6129	$230.61	$230.60	$230.60
7 purchase totals =	$1,063.71		$1,143.5332	$1,143.53	$1,143.55	$1,143.40