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	$123.25	12.427%	$138.5663	$138.57	$138.55	$138.60
Purchase #2	$60.46	12.521%	$68.0302	$68.03	$68.05	$68.00
Purchase #3	$118.40	7.295%	$127.0373	$127.04	$127.05	$127.00
Purchase #4	$32.57	13.758%	$37.051	$37.05	$37.05	$37.10
Purchase #5	$133.43	7.510%	$143.4506	$143.45	$143.45	$143.50
Purchase #6	$59.54	8.480%	$64.589	$64.59	$64.60	$64.60
Purchase #7	$72.58	9.553%	$79.5136	$79.51	$79.50	$79.50
7 purchase totals =	$600.23		$658.2380	$658.24	$658.25	$658.30