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	$15.93	10.458%	$17.596	$17.60	$17.60	$17.60
Purchase #2	$79.39	4.583%	$83.0284	$83.03	$83.05	$83.00
Purchase #3	$240.86	13.723%	$273.9132	$273.91	$273.90	$273.90
Purchase #4	$135.68	10.628%	$150.1001	$150.10	$150.10	$150.10
Purchase #5	$53.64	13.477%	$60.8691	$60.87	$60.85	$60.90
Purchase #6	$62.63	13.473%	$71.0681	$71.07	$71.05	$71.10
Purchase #7	$136.91	5.363%	$144.2525	$144.25	$144.25	$144.30
7 purchase totals =	$725.04		$800.8274	$800.83	$800.80	$800.90