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	$34.95	5.804%	$36.9785	$36.98	$37.00	$37.00
Purchase #2	$241.26	12.238%	$270.7854	$270.79	$270.80	$270.80
Purchase #3	$23.35	6.844%	$24.9481	$24.95	$24.95	$24.90
Purchase #4	$32.38	3.599%	$33.5454	$33.55	$33.55	$33.50
Purchase #5	$19.83	12.319%	$22.2729	$22.27	$22.25	$22.30
Purchase #6	$144.66	5.570%	$152.7176	$152.72	$152.70	$152.70
Purchase #7	$196.35	10.823%	$217.601	$217.60	$217.60	$217.60
7 purchase totals =	$692.78		$758.8489	$758.86	$758.85	$758.80