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	$139.71	6.355%	$148.5886	$148.59	$148.60	$148.60
Purchase #2	$97.72	9.433%	$106.9379	$106.94	$106.95	$106.90
Purchase #3	$136.57	6.772%	$145.8185	$145.82	$145.80	$145.80
Purchase #4	$245.52	5.691%	$259.4925	$259.49	$259.50	$259.50
Purchase #5	$28.79	3.414%	$29.7729	$29.77	$29.75	$29.80
Purchase #6	$128.92	11.554%	$143.8154	$143.82	$143.80	$143.80
Purchase #7	$132.93	8.343%	$144.0203	$144.02	$144.00	$144.00
7 purchase totals =	$910.16		$978.4461	$978.45	$978.40	$978.40