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	$140.60	13.793%	$159.993	$159.99	$160.00	$160.00
Purchase #2	$178.28	10.392%	$196.8069	$196.81	$196.80	$196.80
Purchase #3	$28.84	10.726%	$31.9334	$31.93	$31.95	$31.90
Purchase #4	$165.33	4.168%	$172.221	$172.22	$172.20	$172.20
Purchase #5	$168.67	8.444%	$182.9125	$182.91	$182.90	$182.90
Purchase #6	$184.42	11.209%	$205.0916	$205.09	$205.10	$205.10
Purchase #7	$156.67	6.870%	$167.4332	$167.43	$167.45	$167.40
7 purchase totals =	$1,022.81		$1,116.3916	$1,116.38	$1,116.40	$1,116.30