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	$39.94	4.664%	$41.8028	$41.80	$41.80	$41.80
Purchase #2	$229.73	11.381%	$255.8756	$255.88	$255.90	$255.90
Purchase #3	$38.37	13.575%	$43.5787	$43.58	$43.60	$43.60
Purchase #4	$24.95	12.297%	$28.0181	$28.02	$28.00	$28.00
Purchase #5	$176.92	7.617%	$190.396	$190.40	$190.40	$190.40
Purchase #6	$58.82	11.778%	$65.7478	$65.75	$65.75	$65.70
Purchase #7	$218.40	3.283%	$225.5701	$225.57	$225.55	$225.60
7 purchase totals =	$787.13		$850.9891	$851.00	$851.00	$851.00