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	$246.70	4.783%	$258.4997	$258.50	$258.50	$258.50
Purchase #2	$51.60	9.395%	$56.4478	$56.45	$56.45	$56.40
Purchase #3	$12.47	7.197%	$13.3675	$13.37	$13.35	$13.40
Purchase #4	$178.42	4.419%	$186.3044	$186.30	$186.30	$186.30
Purchase #5	$238.68	13.508%	$270.9209	$270.92	$270.90	$270.90
Purchase #6	$221.35	13.566%	$251.3783	$251.38	$251.40	$251.40
Purchase #7	$37.95	9.156%	$41.4247	$41.42	$41.40	$41.40
7 purchase totals =	$987.17		$1,078.3433	$1,078.34	$1,078.30	$1,078.30