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	$102.95	6.248%	$109.3823	$109.38	$109.40	$109.40
Purchase #2	$78.71	10.744%	$87.1666	$87.17	$87.15	$87.20
Purchase #3	$93.51	6.138%	$99.2496	$99.25	$99.25	$99.20
Purchase #4	$143.29	11.849%	$160.2684	$160.27	$160.25	$160.30
Purchase #5	$138.77	3.463%	$143.5756	$143.58	$143.60	$143.60
Purchase #6	$186.27	3.141%	$192.1207	$192.12	$192.10	$192.10
Purchase #7	$146.93	3.371%	$151.883	$151.88	$151.90	$151.90
7 purchase totals =	$890.43		$943.6462	$943.65	$943.65	$943.70