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	$201.36	3.602%	$208.613	$208.61	$208.60	$208.60
Purchase #2	$135.72	13.373%	$153.8698	$153.87	$153.85	$153.90
Purchase #3	$216.36	6.685%	$230.8237	$230.82	$230.80	$230.80
Purchase #4	$131.44	4.717%	$137.64	$137.64	$137.65	$137.60
Purchase #5	$190.38	7.244%	$204.1711	$204.17	$204.15	$204.20
Purchase #6	$72.29	8.536%	$78.4607	$78.46	$78.45	$78.50
Purchase #7	$76.54	13.279%	$86.7037	$86.70	$86.70	$86.70
7 purchase totals =	$1,024.09		$1,100.2820	$1,100.27	$1,100.20	$1,100.30