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	$75.82	6.857%	$81.019	$81.02	$81.00	$81.00
Purchase #2	$127.97	12.298%	$143.7078	$143.71	$143.70	$143.70
Purchase #3	$153.64	9.438%	$168.1405	$168.14	$168.15	$168.10
Purchase #4	$193.27	3.487%	$200.0093	$200.01	$200.00	$200.00
Purchase #5	$151.25	6.321%	$160.8105	$160.81	$160.80	$160.80
Purchase #6	$24.43	6.104%	$25.9212	$25.92	$25.90	$25.90
Purchase #7	$109.64	8.464%	$118.9199	$118.92	$118.90	$118.90
7 purchase totals =	$836.02		$898.5282	$898.53	$898.45	$898.40