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	$91.94	13.769%	$104.5992	$104.60	$104.60	$104.60
Purchase #2	$155.55	5.300%	$163.7942	$163.79	$163.80	$163.80
Purchase #3	$205.52	11.197%	$228.5321	$228.53	$228.55	$228.50
Purchase #4	$94.99	4.852%	$99.5989	$99.60	$99.60	$99.60
Purchase #5	$248.56	10.517%	$274.7011	$274.70	$274.70	$274.70
Purchase #6	$167.80	8.709%	$182.4137	$182.41	$182.40	$182.40
Purchase #7	$151.98	11.150%	$168.9258	$168.93	$168.95	$168.90
7 purchase totals =	$1,116.34		$1,222.5650	$1,222.56	$1,222.60	$1,222.50