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	$38.88	4.373%	$40.5802	$40.58	$40.60	$40.60
Purchase #2	$32.75	13.664%	$37.225	$37.23	$37.25	$37.20
Purchase #3	$14.98	12.672%	$16.8783	$16.88	$16.90	$16.90
Purchase #4	$233.64	5.657%	$246.857	$246.86	$246.85	$246.90
Purchase #5	$179.48	6.349%	$190.8752	$190.88	$190.90	$190.90
Purchase #6	$94.79	13.400%	$107.4919	$107.49	$107.50	$107.50
Purchase #7	$67.65	7.112%	$72.4613	$72.46	$72.45	$72.50
7 purchase totals =	$662.17		$712.3689	$712.38	$712.45	$712.50