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	$132.45	5.377%	$139.5718	$139.57	$139.55	$139.60
Purchase #2	$110.93	13.436%	$125.8346	$125.83	$125.85	$125.80
Purchase #3	$186.55	6.491%	$198.659	$198.66	$198.65	$198.70
Purchase #4	$98.30	7.727%	$105.8956	$105.90	$105.90	$105.90
Purchase #5	$95.70	5.313%	$100.7845	$100.78	$100.80	$100.80
Purchase #6	$100.30	10.704%	$111.0361	$111.04	$111.05	$111.00
Purchase #7	$156.84	9.835%	$172.2652	$172.27	$172.25	$172.30
7 purchase totals =	$881.07		$954.0468	$954.05	$954.05	$954.10