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	$167.79	10.794%	$185.9013	$185.90	$185.90	$185.90
Purchase #2	$103.43	9.652%	$113.4131	$113.41	$113.40	$113.40
Purchase #3	$123.94	12.480%	$139.4077	$139.41	$139.40	$139.40
Purchase #4	$157.67	11.169%	$175.2802	$175.28	$175.30	$175.30
Purchase #5	$24.67	11.304%	$27.4587	$27.46	$27.45	$27.50
Purchase #6	$195.28	7.325%	$209.5843	$209.58	$209.60	$209.60
Purchase #7	$210.25	9.465%	$230.1502	$230.15	$230.15	$230.20
7 purchase totals =	$983.03		$1,081.1955	$1,081.19	$1,081.20	$1,081.30