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	$36.54	6.357%	$38.8628	$38.86	$38.85	$38.90
Purchase #2	$99.51	10.737%	$110.1944	$110.19	$110.20	$110.20
Purchase #3	$139.87	12.132%	$156.839	$156.84	$156.85	$156.80
Purchase #4	$241.84	5.575%	$255.3226	$255.32	$255.30	$255.30
Purchase #5	$163.31	13.806%	$185.8566	$185.86	$185.85	$185.90
Purchase #6	$142.50	8.328%	$154.3674	$154.37	$154.35	$154.40
Purchase #7	$120.33	10.680%	$133.1812	$133.18	$133.20	$133.20
7 purchase totals =	$943.90		$1,034.6240	$1,034.62	$1,034.60	$1,034.70