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	$155.36	10.249%	$171.2828	$171.28	$171.30	$171.30
Purchase #2	$95.88	7.467%	$103.0394	$103.04	$103.05	$103.00
Purchase #3	$213.34	6.601%	$227.4226	$227.42	$227.40	$227.40
Purchase #4	$47.88	9.668%	$52.509	$52.51	$52.50	$52.50
Purchase #5	$219.32	8.735%	$238.4776	$238.48	$238.50	$238.50
Purchase #6	$58.90	13.135%	$66.6365	$66.64	$66.65	$66.60
Purchase #7	$23.72	5.435%	$25.0092	$25.01	$25.00	$25.00
7 purchase totals =	$814.40		$884.3771	$884.38	$884.40	$884.30