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	$132.78	10.390%	$146.5758	$146.58	$146.60	$146.60
Purchase #2	$25.65	7.121%	$27.4765	$27.48	$27.50	$27.50
Purchase #3	$79.28	4.216%	$82.6224	$82.62	$82.60	$82.60
Purchase #4	$160.53	11.203%	$178.5142	$178.51	$178.50	$178.50
Purchase #5	$222.54	11.711%	$248.6017	$248.60	$248.60	$248.60
Purchase #6	$82.94	3.455%	$85.8056	$85.81	$85.80	$85.80
Purchase #7	$161.95	4.497%	$169.2329	$169.23	$169.25	$169.20
7 purchase totals =	$865.67		$938.8291	$938.83	$938.85	$938.80