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	$25.61	13.828%	$29.1514	$29.15	$29.15	$29.20
Purchase #2	$169.94	9.571%	$186.205	$186.21	$186.20	$186.20
Purchase #3	$142.92	9.514%	$156.5174	$156.52	$156.50	$156.50
Purchase #4	$153.88	4.263%	$160.4399	$160.44	$160.45	$160.40
Purchase #5	$59.90	10.544%	$66.2159	$66.22	$66.20	$66.20
Purchase #6	$79.53	5.124%	$83.6051	$83.61	$83.60	$83.60
Purchase #7	$126.30	8.856%	$137.4851	$137.49	$137.50	$137.50
7 purchase totals =	$758.08		$819.6198	$819.64	$819.60	$819.60