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	$38.76	3.786%	$40.2275	$40.23	$40.25	$40.20
Purchase #2	$241.28	10.573%	$266.7905	$266.79	$266.80	$266.80
Purchase #3	$80.42	12.843%	$90.7483	$90.75	$90.75	$90.70
Purchase #4	$196.42	8.516%	$213.1471	$213.15	$213.15	$213.10
Purchase #5	$134.29	11.781%	$150.1107	$150.11	$150.10	$150.10
Purchase #6	$219.93	4.858%	$230.6142	$230.61	$230.60	$230.60
Purchase #7	$249.97	5.116%	$262.7585	$262.76	$262.75	$262.80
7 purchase totals =	$1,161.07		$1,254.3968	$1,254.40	$1,254.40	$1,254.30