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	$78.68	4.547%	$82.2576	$82.26	$82.25	$82.30
Purchase #2	$29.58	8.452%	$32.0801	$32.08	$32.10	$32.10
Purchase #3	$152.96	9.843%	$168.0159	$168.02	$168.00	$168.00
Purchase #4	$83.28	9.722%	$91.3765	$91.38	$91.40	$91.40
Purchase #5	$95.70	13.616%	$108.7305	$108.73	$108.75	$108.70
Purchase #6	$24.40	13.665%	$27.7343	$27.73	$27.75	$27.70
Purchase #7	$90.70	4.295%	$94.5956	$94.60	$94.60	$94.60
7 purchase totals =	$555.30		$604.7905	$604.80	$604.85	$604.80