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	$185.42	3.682%	$192.2472	$192.25	$192.25	$192.20
Purchase #2	$95.51	4.271%	$99.5892	$99.59	$99.60	$99.60
Purchase #3	$87.72	13.808%	$99.8324	$99.83	$99.85	$99.80
Purchase #4	$56.32	9.651%	$61.7554	$61.76	$61.75	$61.80
Purchase #5	$81.30	7.622%	$87.4967	$87.50	$87.50	$87.50
Purchase #6	$16.83	8.715%	$18.2967	$18.30	$18.30	$18.30
Purchase #7	$250.59	12.864%	$282.8259	$282.83	$282.85	$282.80
7 purchase totals =	$773.69		$842.0435	$842.06	$842.10	$842.00