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	$147.38	8.171%	$159.4224	$159.42	$159.40	$159.40
Purchase #2	$226.52	12.619%	$255.1046	$255.10	$255.10	$255.10
Purchase #3	$20.88	6.361%	$22.2082	$22.21	$22.20	$22.20
Purchase #4	$36.33	10.648%	$40.1984	$40.20	$40.20	$40.20
Purchase #5	$134.33	3.820%	$139.4614	$139.46	$139.45	$139.50
Purchase #6	$49.97	9.697%	$54.8156	$54.82	$54.80	$54.80
Purchase #7	$11.72	13.842%	$13.3423	$13.34	$13.35	$13.30
7 purchase totals =	$627.13		$684.5529	$684.55	$684.50	$684.50