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	$139.96	4.141%	$145.7557	$145.76	$145.75	$145.80
Purchase #2	$37.27	8.338%	$40.3776	$40.38	$40.40	$40.40
Purchase #3	$166.32	9.114%	$181.4784	$181.48	$181.50	$181.50
Purchase #4	$122.30	9.569%	$134.0029	$134.00	$134.00	$134.00
Purchase #5	$95.96	11.105%	$106.6164	$106.62	$106.60	$106.60
Purchase #6	$94.89	9.552%	$103.9539	$103.95	$103.95	$104.00
Purchase #7	$65.61	10.492%	$72.4938	$72.49	$72.50	$72.50
7 purchase totals =	$722.31		$784.6787	$784.68	$784.70	$784.80