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	$157.26	5.826%	$166.422	$166.42	$166.40	$166.40
Purchase #2	$104.97	3.706%	$108.8602	$108.86	$108.85	$108.90
Purchase #3	$227.62	12.219%	$255.4329	$255.43	$255.45	$255.40
Purchase #4	$118.88	12.811%	$134.1097	$134.11	$134.10	$134.10
Purchase #5	$192.72	5.495%	$203.31	$203.31	$203.30	$203.30
Purchase #6	$156.77	7.358%	$168.3051	$168.31	$168.30	$168.30
Purchase #7	$40.98	13.663%	$46.5791	$46.58	$46.60	$46.60
7 purchase totals =	$999.20		$1,083.0190	$1,083.02	$1,083.00	$1,083.00