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	$132.73	4.339%	$138.4892	$138.49	$138.50	$138.50
Purchase #2	$143.32	4.509%	$149.7823	$149.78	$149.80	$149.80
Purchase #3	$199.32	10.181%	$219.6128	$219.61	$219.60	$219.60
Purchase #4	$139.86	11.513%	$155.9621	$155.96	$155.95	$156.00
Purchase #5	$169.56	13.168%	$191.8877	$191.89	$191.90	$191.90
Purchase #6	$23.62	3.587%	$24.4672	$24.47	$24.45	$24.50
Purchase #7	$94.86	6.270%	$100.8077	$100.81	$100.80	$100.80
7 purchase totals =	$903.27		$981.0090	$981.01	$981.00	$981.10