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	$101.94	13.407%	$115.6071	$115.61	$115.60	$115.60
Purchase #2	$72.54	10.565%	$80.2039	$80.20	$80.20	$80.20
Purchase #3	$132.84	13.628%	$150.9434	$150.94	$150.95	$150.90
Purchase #4	$227.59	6.297%	$241.9213	$241.92	$241.90	$241.90
Purchase #5	$81.74	4.442%	$85.3709	$85.37	$85.35	$85.40
Purchase #6	$177.69	4.618%	$185.8957	$185.90	$185.90	$185.90
Purchase #7	$15.95	9.760%	$17.5067	$17.51	$17.50	$17.50
7 purchase totals =	$810.29		$877.4490	$877.45	$877.40	$877.40