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	$8.77	13.102%	$9.919	$9.92	$9.90	$9.90
Purchase #2	$103.30	7.643%	$111.1952	$111.20	$111.20	$111.20
Purchase #3	$126.48	10.306%	$139.515	$139.52	$139.50	$139.50
Purchase #4	$72.34	13.134%	$81.8411	$81.84	$81.85	$81.80
Purchase #5	$141.25	8.247%	$152.8989	$152.90	$152.90	$152.90
Purchase #6	$139.37	8.440%	$151.1328	$151.13	$151.15	$151.10
Purchase #7	$51.52	7.385%	$55.3248	$55.32	$55.30	$55.30
7 purchase totals =	$643.03		$701.8268	$701.83	$701.80	$701.70