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	$132.25	5.459%	$139.4695	$139.47	$139.45	$139.50
Purchase #2	$214.94	10.295%	$237.0681	$237.07	$237.05	$237.10
Purchase #3	$39.26	11.524%	$43.7843	$43.78	$43.80	$43.80
Purchase #4	$83.29	8.776%	$90.5995	$90.60	$90.60	$90.60
Purchase #5	$98.87	7.390%	$106.1765	$106.18	$106.20	$106.20
Purchase #6	$231.50	7.848%	$249.6681	$249.67	$249.65	$249.70
Purchase #7	$100.73	8.262%	$109.0523	$109.05	$109.05	$109.10
7 purchase totals =	$900.84		$975.8183	$975.82	$975.80	$976.00