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	$91.65	9.285%	$100.1597	$100.16	$100.15	$100.20
Purchase #2	$196.47	13.408%	$222.8127	$222.81	$222.80	$222.80
Purchase #3	$95.90	7.449%	$103.0436	$103.04	$103.05	$103.00
Purchase #4	$48.28	7.709%	$52.0019	$52.00	$52.00	$52.00
Purchase #5	$246.48	4.139%	$256.6818	$256.68	$256.70	$256.70
Purchase #6	$14.94	11.527%	$16.6621	$16.66	$16.65	$16.70
Purchase #7	$96.50	9.321%	$105.4948	$105.49	$105.50	$105.50
7 purchase totals =	$790.22		$856.8566	$856.84	$856.85	$856.90