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	$44.40	9.258%	$48.5106	$48.51	$48.50	$48.50
Purchase #2	$235.38	7.206%	$252.3415	$252.34	$252.35	$252.30
Purchase #3	$205.57	3.853%	$213.4906	$213.49	$213.50	$213.50
Purchase #4	$106.66	4.638%	$111.6069	$111.61	$111.60	$111.60
Purchase #5	$148.77	6.548%	$158.5115	$158.51	$158.50	$158.50
Purchase #6	$195.86	5.387%	$206.411	$206.41	$206.40	$206.40
Purchase #7	$94.71	6.197%	$100.5792	$100.58	$100.60	$100.60
7 purchase totals =	$1,031.35		$1,091.4513	$1,091.45	$1,091.45	$1,091.40