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	$104.56	13.308%	$118.4748	$118.47	$118.45	$118.50
Purchase #2	$248.51	4.335%	$259.2829	$259.28	$259.30	$259.30
Purchase #3	$36.81	12.319%	$41.3446	$41.34	$41.35	$41.30
Purchase #4	$217.28	10.691%	$240.5094	$240.51	$240.50	$240.50
Purchase #5	$132.85	3.464%	$137.4519	$137.45	$137.45	$137.50
Purchase #6	$46.95	11.298%	$52.2544	$52.25	$52.25	$52.30
Purchase #7	$77.51	11.790%	$86.6484	$86.65	$86.65	$86.60
7 purchase totals =	$864.47		$935.9664	$935.95	$935.95	$936.00