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	$146.98	8.847%	$159.9833	$159.98	$160.00	$160.00
Purchase #2	$196.25	9.640%	$215.1685	$215.17	$215.15	$215.20
Purchase #3	$83.86	3.242%	$86.5787	$86.58	$86.60	$86.60
Purchase #4	$40.84	5.174%	$42.9531	$42.95	$42.95	$43.00
Purchase #5	$31.49	4.794%	$32.9996	$33.00	$33.00	$33.00
Purchase #6	$249.30	12.361%	$280.116	$280.12	$280.10	$280.10
Purchase #7	$52.38	4.268%	$54.6156	$54.62	$54.60	$54.60
7 purchase totals =	$801.10		$872.4148	$872.42	$872.40	$872.50