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	$131.92	5.705%	$139.446	$139.45	$139.45	$139.40
Purchase #2	$43.33	6.484%	$46.1395	$46.14	$46.15	$46.10
Purchase #3	$197.68	8.570%	$214.6212	$214.62	$214.60	$214.60
Purchase #4	$37.82	8.127%	$40.8936	$40.89	$40.90	$40.90
Purchase #5	$206.70	11.246%	$229.9455	$229.95	$229.95	$229.90
Purchase #6	$236.38	5.172%	$248.6056	$248.61	$248.60	$248.60
Purchase #7	$16.67	11.616%	$18.6064	$18.61	$18.60	$18.60
7 purchase totals =	$870.50		$938.2578	$938.27	$938.25	$938.10