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	$48.67	5.348%	$51.2729	$51.27	$51.25	$51.30
Purchase #2	$92.88	7.691%	$100.0234	$100.02	$100.00	$100.00
Purchase #3	$10.29	12.508%	$11.5771	$11.58	$11.60	$11.60
Purchase #4	$102.44	8.402%	$111.047	$111.05	$111.05	$111.00
Purchase #5	$160.45	7.209%	$172.0168	$172.02	$172.00	$172.00
Purchase #6	$43.33	3.501%	$44.847	$44.85	$44.85	$44.80
Purchase #7	$164.98	12.641%	$185.8351	$185.84	$185.85	$185.80
7 purchase totals =	$623.04		$676.6193	$676.63	$676.60	$676.50