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	$54.59	8.849%	$59.4207	$59.42	$59.40	$59.40
Purchase #2	$52.58	12.275%	$59.0342	$59.03	$59.05	$59.00
Purchase #3	$148.91	4.478%	$155.5782	$155.58	$155.60	$155.60
Purchase #4	$37.51	4.194%	$39.0832	$39.08	$39.10	$39.10
Purchase #5	$98.90	6.583%	$105.4106	$105.41	$105.40	$105.40
Purchase #6	$205.57	13.641%	$233.6118	$233.61	$233.60	$233.60
Purchase #7	$75.52	10.838%	$83.7049	$83.70	$83.70	$83.70
7 purchase totals =	$673.58		$735.8436	$735.83	$735.85	$735.80