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	$127.29	9.328%	$139.1636	$139.16	$139.15	$139.20
Purchase #2	$232.71	9.758%	$255.4178	$255.42	$255.40	$255.40
Purchase #3	$85.40	4.438%	$89.1901	$89.19	$89.20	$89.20
Purchase #4	$50.76	6.357%	$53.9868	$53.99	$54.00	$54.00
Purchase #5	$164.66	5.136%	$173.1169	$173.12	$173.10	$173.10
Purchase #6	$201.38	11.844%	$225.2314	$225.23	$225.25	$225.20
Purchase #7	$213.92	4.167%	$222.834	$222.83	$222.85	$222.80
7 purchase totals =	$1,076.12		$1,158.9406	$1,158.94	$1,158.95	$1,158.90