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	$128.81	11.201%	$143.238	$143.24	$143.25	$143.20
Purchase #2	$137.79	3.691%	$142.8758	$142.88	$142.90	$142.90
Purchase #3	$121.58	4.496%	$127.0462	$127.05	$127.05	$127.00
Purchase #4	$139.25	9.314%	$152.2197	$152.22	$152.20	$152.20
Purchase #5	$192.27	12.707%	$216.7017	$216.70	$216.70	$216.70
Purchase #6	$156.29	10.294%	$172.3785	$172.38	$172.40	$172.40
Purchase #7	$221.44	3.356%	$228.8715	$228.87	$228.85	$228.90
7 purchase totals =	$1,097.43		$1,183.3314	$1,183.34	$1,183.35	$1,183.30