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	$133.94	7.872%	$144.4838	$144.48	$144.50	$144.50
Purchase #2	$163.76	5.493%	$172.7553	$172.76	$172.75	$172.80
Purchase #3	$103.83	5.574%	$109.6175	$109.62	$109.60	$109.60
Purchase #4	$58.43	8.707%	$63.5175	$63.52	$63.50	$63.50
Purchase #5	$121.58	4.801%	$127.4171	$127.42	$127.40	$127.40
Purchase #6	$19.77	10.688%	$21.883	$21.88	$21.90	$21.90
Purchase #7	$77.47	7.480%	$83.2648	$83.26	$83.25	$83.30
7 purchase totals =	$678.78		$722.9390	$722.94	$722.90	$723.00