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	$35.79	4.649%	$37.4539	$37.45	$37.45	$37.50
Purchase #2	$52.32	4.719%	$54.789	$54.79	$54.80	$54.80
Purchase #3	$143.79	13.550%	$163.2735	$163.27	$163.25	$163.30
Purchase #4	$83.66	3.792%	$86.8324	$86.83	$86.85	$86.80
Purchase #5	$141.58	13.374%	$160.5149	$160.51	$160.50	$160.50
Purchase #6	$130.34	5.697%	$137.7655	$137.77	$137.75	$137.80
Purchase #7	$246.85	4.852%	$258.8272	$258.83	$258.85	$258.80
7 purchase totals =	$834.33		$899.4564	$899.45	$899.45	$899.50