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	$108.85	4.400%	$113.6394	$113.64	$113.65	$113.60
Purchase #2	$132.97	9.292%	$145.3256	$145.33	$145.35	$145.30
Purchase #3	$110.56	12.106%	$123.9444	$123.94	$123.95	$123.90
Purchase #4	$34.78	7.801%	$37.4932	$37.49	$37.50	$37.50
Purchase #5	$128.52	11.663%	$143.5093	$143.51	$143.50	$143.50
Purchase #6	$152.62	6.668%	$162.7967	$162.80	$162.80	$162.80
Purchase #7	$186.45	7.252%	$199.9714	$199.97	$199.95	$200.00
7 purchase totals =	$854.75		$926.6800	$926.68	$926.70	$926.60