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	$60.35	9.723%	$66.2178	$66.22	$66.20	$66.20
Purchase #2	$245.41	6.304%	$260.8806	$260.88	$260.90	$260.90
Purchase #3	$161.53	7.481%	$173.6141	$173.61	$173.60	$173.60
Purchase #4	$143.83	10.650%	$159.1479	$159.15	$159.15	$159.10
Purchase #5	$207.25	13.202%	$234.6111	$234.61	$234.60	$234.60
Purchase #6	$34.94	6.241%	$37.1206	$37.12	$37.10	$37.10
Purchase #7	$156.29	8.281%	$169.2324	$169.23	$169.25	$169.20
7 purchase totals =	$1,009.60		$1,100.8245	$1,100.82	$1,100.80	$1,100.70