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	$94.55	5.230%	$99.495	$99.50	$99.50	$99.50
Purchase #2	$177.78	6.553%	$189.4299	$189.43	$189.45	$189.40
Purchase #3	$142.37	9.564%	$155.9863	$155.99	$156.00	$156.00
Purchase #4	$81.78	4.390%	$85.3701	$85.37	$85.35	$85.40
Purchase #5	$132.64	10.180%	$146.1428	$146.14	$146.15	$146.10
Purchase #6	$65.38	5.327%	$68.8628	$68.86	$68.85	$68.90
Purchase #7	$155.54	8.356%	$168.5369	$168.54	$168.55	$168.50
7 purchase totals =	$850.04		$913.8238	$913.83	$913.85	$913.80