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	$18.37	9.697%	$20.1513	$20.15	$20.15	$20.20
Purchase #2	$43.37	10.442%	$47.8987	$47.90	$47.90	$47.90
Purchase #3	$121.54	8.842%	$132.2866	$132.29	$132.30	$132.30
Purchase #4	$41.93	8.461%	$45.4777	$45.48	$45.50	$45.50
Purchase #5	$242.52	12.476%	$272.7768	$272.78	$272.80	$272.80
Purchase #6	$50.86	6.792%	$54.3144	$54.31	$54.30	$54.30
Purchase #7	$170.45	10.285%	$187.9808	$187.98	$188.00	$188.00
7 purchase totals =	$689.04		$760.8863	$760.89	$760.95	$761.00