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	$215.53	11.142%	$239.5444	$239.54	$239.55	$239.50
Purchase #2	$162.86	5.676%	$172.1039	$172.10	$172.10	$172.10
Purchase #3	$156.58	5.721%	$165.5379	$165.54	$165.55	$165.50
Purchase #4	$72.31	12.646%	$81.4543	$81.45	$81.45	$81.50
Purchase #5	$54.86	9.168%	$59.8896	$59.89	$59.90	$59.90
Purchase #6	$31.75	7.636%	$34.1744	$34.17	$34.15	$34.20
Purchase #7	$100.50	3.668%	$104.1863	$104.19	$104.20	$104.20
7 purchase totals =	$794.39		$856.8908	$856.88	$856.90	$856.90