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	$171.90	8.140%	$185.8927	$185.89	$185.90	$185.90
Purchase #2	$145.69	12.803%	$164.3427	$164.34	$164.35	$164.30
Purchase #3	$61.58	3.722%	$63.872	$63.87	$63.85	$63.90
Purchase #4	$116.60	5.695%	$123.2404	$123.24	$123.25	$123.20
Purchase #5	$43.76	12.628%	$49.286	$49.29	$49.30	$49.30
Purchase #6	$151.54	11.333%	$168.714	$168.71	$168.70	$168.70
Purchase #7	$214.67	8.585%	$233.0994	$233.10	$233.10	$233.10
7 purchase totals =	$905.74		$988.4472	$988.44	$988.45	$988.40