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	$246.54	13.175%	$279.0216	$279.02	$279.00	$279.00
Purchase #2	$42.83	6.345%	$45.5476	$45.55	$45.55	$45.50
Purchase #3	$85.53	4.707%	$89.5559	$89.56	$89.55	$89.60
Purchase #4	$119.42	7.265%	$128.0959	$128.10	$128.10	$128.10
Purchase #5	$176.70	8.866%	$192.3662	$192.37	$192.35	$192.40
Purchase #6	$179.67	8.128%	$194.2736	$194.27	$194.25	$194.30
Purchase #7	$61.55	8.609%	$66.8488	$66.85	$66.85	$66.80
7 purchase totals =	$912.24		$995.7096	$995.72	$995.65	$995.70