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	$26.42	7.584%	$28.4237	$28.42	$28.40	$28.40
Purchase #2	$200.69	7.789%	$216.3217	$216.32	$216.30	$216.30
Purchase #3	$239.52	13.318%	$271.4193	$271.42	$271.40	$271.40
Purchase #4	$141.46	7.334%	$151.8347	$151.83	$151.85	$151.80
Purchase #5	$103.80	13.580%	$117.896	$117.90	$117.90	$117.90
Purchase #6	$92.91	12.113%	$104.1642	$104.16	$104.15	$104.20
Purchase #7	$40.43	6.304%	$42.9787	$42.98	$43.00	$43.00
7 purchase totals =	$845.23		$933.0383	$933.03	$933.00	$933.00