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	$63.50	5.196%	$66.7995	$66.80	$66.80	$66.80
Purchase #2	$224.98	5.802%	$238.0333	$238.03	$238.05	$238.00
Purchase #3	$158.95	10.464%	$175.5825	$175.58	$175.60	$175.60
Purchase #4	$183.29	4.291%	$191.155	$191.16	$191.15	$191.20
Purchase #5	$82.60	4.403%	$86.2369	$86.24	$86.25	$86.20
Purchase #6	$175.61	9.123%	$191.6309	$191.63	$191.65	$191.60
Purchase #7	$248.63	10.155%	$273.8784	$273.88	$273.90	$273.90
7 purchase totals =	$1,137.56		$1,223.3165	$1,223.32	$1,223.40	$1,223.30