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	$33.82	10.873%	$37.4972	$37.50	$37.50	$37.50
Purchase #2	$69.61	3.669%	$72.164	$72.16	$72.15	$72.20
Purchase #3	$29.38	7.263%	$31.5139	$31.51	$31.50	$31.50
Purchase #4	$59.54	11.176%	$66.1942	$66.19	$66.20	$66.20
Purchase #5	$98.36	5.700%	$103.9665	$103.97	$103.95	$104.00
Purchase #6	$72.56	11.273%	$80.7397	$80.74	$80.75	$80.70
Purchase #7	$141.59	3.472%	$146.506	$146.51	$146.50	$146.50
7 purchase totals =	$504.86		$538.5815	$538.58	$538.55	$538.60