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	$106.85	13.176%	$120.9286	$120.93	$120.95	$120.90
Purchase #2	$36.77	6.820%	$39.2777	$39.28	$39.30	$39.30
Purchase #3	$137.73	6.363%	$146.4938	$146.49	$146.50	$146.50
Purchase #4	$16.32	12.280%	$18.3241	$18.32	$18.30	$18.30
Purchase #5	$108.36	10.288%	$119.5081	$119.51	$119.50	$119.50
Purchase #6	$91.96	7.629%	$98.9756	$98.98	$99.00	$99.00
Purchase #7	$155.83	12.461%	$175.248	$175.25	$175.25	$175.20
7 purchase totals =	$653.82		$718.7559	$718.76	$718.80	$718.70