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	$204.34	5.393%	$215.3601	$215.36	$215.35	$215.40
Purchase #2	$125.45	7.201%	$134.4837	$134.48	$134.50	$134.50
Purchase #3	$100.41	10.761%	$111.2151	$111.22	$111.20	$111.20
Purchase #4	$19.86	8.324%	$21.5131	$21.51	$21.50	$21.50
Purchase #5	$120.63	6.792%	$128.8232	$128.82	$128.80	$128.80
Purchase #6	$237.93	9.762%	$261.1567	$261.16	$261.15	$261.20
Purchase #7	$106.27	12.714%	$119.7812	$119.78	$119.80	$119.80
7 purchase totals =	$914.89		$992.3331	$992.33	$992.30	$992.40