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	$88.75	12.226%	$99.6006	$99.60	$99.60	$99.60
Purchase #2	$194.51	5.583%	$205.3695	$205.37	$205.35	$205.40
Purchase #3	$158.55	11.560%	$176.8784	$176.88	$176.90	$176.90
Purchase #4	$150.41	5.589%	$158.8164	$158.82	$158.80	$158.80
Purchase #5	$85.41	12.382%	$95.9855	$95.99	$96.00	$96.00
Purchase #6	$66.68	9.295%	$72.8779	$72.88	$72.90	$72.90
Purchase #7	$135.69	11.872%	$151.7991	$151.80	$151.80	$151.80
7 purchase totals =	$880.00		$961.3274	$961.34	$961.35	$961.40