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	$118.51	9.528%	$129.8016	$129.80	$129.80	$129.80
Purchase #2	$131.63	7.778%	$141.8682	$141.87	$141.85	$141.90
Purchase #3	$249.86	3.590%	$258.83	$258.83	$258.85	$258.80
Purchase #4	$113.32	11.433%	$126.2759	$126.28	$126.30	$126.30
Purchase #5	$227.87	13.384%	$258.3681	$258.37	$258.35	$258.40
Purchase #6	$38.83	4.323%	$40.5086	$40.51	$40.50	$40.50
Purchase #7	$54.48	10.432%	$60.1634	$60.16	$60.15	$60.20
7 purchase totals =	$934.50		$1,015.8158	$1,015.82	$1,015.80	$1,015.90