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	$40.76	4.430%	$42.5657	$42.57	$42.55	$42.60
Purchase #2	$114.65	10.792%	$127.023	$127.02	$127.00	$127.00
Purchase #3	$136.39	5.376%	$143.7223	$143.72	$143.70	$143.70
Purchase #4	$10.95	5.508%	$11.5531	$11.55	$11.55	$11.60
Purchase #5	$14.38	4.428%	$15.0167	$15.02	$15.00	$15.00
Purchase #6	$24.32	3.393%	$25.1452	$25.15	$25.15	$25.10
Purchase #7	$16.85	9.732%	$18.4898	$18.49	$18.50	$18.50
7 purchase totals =	$358.30		$383.5158	$383.52	$383.45	$383.50