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	$11.89	11.376%	$13.2426	$13.24	$13.25	$13.20
Purchase #2	$209.47	13.306%	$237.3421	$237.34	$237.35	$237.30
Purchase #3	$165.93	11.246%	$184.5905	$184.59	$184.60	$184.60
Purchase #4	$193.27	13.284%	$218.944	$218.94	$218.95	$218.90
Purchase #5	$109.70	13.463%	$124.4689	$124.47	$124.45	$124.50
Purchase #6	$95.82	9.285%	$104.7169	$104.72	$104.70	$104.70
Purchase #7	$142.50	7.270%	$152.8598	$152.86	$152.85	$152.90
7 purchase totals =	$928.58		$1,036.1648	$1,036.16	$1,036.15	$1,036.10