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	$20.25	4.629%	$21.1874	$21.19	$21.20	$21.20
Purchase #2	$113.85	10.738%	$126.0752	$126.08	$126.10	$126.10
Purchase #3	$201.54	13.712%	$229.1752	$229.18	$229.20	$229.20
Purchase #4	$190.67	10.562%	$210.8086	$210.81	$210.80	$210.80
Purchase #5	$85.95	5.310%	$90.5139	$90.51	$90.50	$90.50
Purchase #6	$106.48	9.549%	$116.6478	$116.65	$116.65	$116.60
Purchase #7	$90.97	10.787%	$100.7829	$100.78	$100.80	$100.80
7 purchase totals =	$809.71		$895.1910	$895.20	$895.25	$895.20