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	$105.42	10.795%	$116.8001	$116.80	$116.80	$116.80
Purchase #2	$89.88	8.395%	$97.4254	$97.43	$97.45	$97.40
Purchase #3	$179.89	12.810%	$202.9339	$202.93	$202.95	$202.90
Purchase #4	$72.49	8.612%	$78.7328	$78.73	$78.75	$78.70
Purchase #5	$81.43	10.536%	$90.0095	$90.01	$90.00	$90.00
Purchase #6	$67.77	6.602%	$72.2442	$72.24	$72.25	$72.20
Purchase #7	$108.59	11.221%	$120.7749	$120.77	$120.75	$120.80
7 purchase totals =	$705.47		$778.9208	$778.91	$778.95	$778.80