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	$127.71	12.309%	$143.4298	$143.43	$143.45	$143.40
Purchase #2	$33.84	9.710%	$37.1259	$37.13	$37.15	$37.10
Purchase #3	$88.34	11.794%	$98.7588	$98.76	$98.75	$98.80
Purchase #4	$139.34	10.189%	$153.5374	$153.54	$153.55	$153.50
Purchase #5	$161.94	3.127%	$167.0039	$167.00	$167.00	$167.00
Purchase #6	$238.95	11.366%	$266.1091	$266.11	$266.10	$266.10
Purchase #7	$20.29	6.708%	$21.6511	$21.65	$21.65	$21.70
7 purchase totals =	$810.41		$887.6160	$887.62	$887.65	$887.60