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	$126.59	12.572%	$142.5049	$142.50	$142.50	$142.50
Purchase #2	$172.39	7.324%	$185.0158	$185.02	$185.00	$185.00
Purchase #3	$85.41	10.207%	$94.1278	$94.13	$94.15	$94.10
Purchase #4	$38.25	10.418%	$42.2349	$42.23	$42.25	$42.20
Purchase #5	$163.49	9.231%	$178.5818	$178.58	$178.60	$178.60
Purchase #6	$89.83	13.571%	$102.0208	$102.02	$102.00	$102.00
Purchase #7	$137.85	4.818%	$144.4916	$144.49	$144.50	$144.50
7 purchase totals =	$813.81		$888.9776	$888.97	$889.00	$888.90