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	$139.50	12.185%	$156.4981	$156.50	$156.50	$156.50
Purchase #2	$127.78	5.307%	$134.5613	$134.56	$134.55	$134.60
Purchase #3	$162.45	13.283%	$184.0282	$184.03	$184.05	$184.00
Purchase #4	$134.54	5.834%	$142.3891	$142.39	$142.40	$142.40
Purchase #5	$194.68	12.622%	$219.2525	$219.25	$219.25	$219.30
Purchase #6	$156.45	5.723%	$165.4036	$165.40	$165.40	$165.40
Purchase #7	$40.98	5.816%	$43.3634	$43.36	$43.35	$43.40
7 purchase totals =	$956.38		$1,045.4962	$1,045.49	$1,045.50	$1,045.60