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	$14.30	8.155%	$15.4662	$15.47	$15.45	$15.50
Purchase #2	$237.58	10.132%	$261.6516	$261.65	$261.65	$261.70
Purchase #3	$89.52	11.814%	$100.0959	$100.10	$100.10	$100.10
Purchase #4	$23.72	7.562%	$25.5137	$25.51	$25.50	$25.50
Purchase #5	$84.34	5.736%	$89.1777	$89.18	$89.20	$89.20
Purchase #6	$36.79	4.759%	$38.5408	$38.54	$38.55	$38.50
Purchase #7	$52.98	10.677%	$58.6367	$58.64	$58.65	$58.60
7 purchase totals =	$539.23		$589.0826	$589.09	$589.10	$589.10