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	$166.65	13.238%	$188.7111	$188.71	$188.70	$188.70
Purchase #2	$106.59	4.695%	$111.5944	$111.59	$111.60	$111.60
Purchase #3	$166.25	7.498%	$178.7154	$178.72	$178.70	$178.70
Purchase #4	$127.48	6.746%	$136.0798	$136.08	$136.10	$136.10
Purchase #5	$143.85	13.564%	$163.3618	$163.36	$163.35	$163.40
Purchase #6	$29.95	8.857%	$32.6027	$32.60	$32.60	$32.60
Purchase #7	$127.85	9.438%	$139.9165	$139.92	$139.90	$139.90
7 purchase totals =	$868.62		$950.9817	$950.98	$950.95	$951.00