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	$87.31	12.772%	$98.4612	$98.46	$98.45	$98.50
Purchase #2	$132.62	7.403%	$142.4379	$142.44	$142.45	$142.40
Purchase #3	$98.74	5.833%	$104.4995	$104.50	$104.50	$104.50
Purchase #4	$47.59	13.103%	$53.8257	$53.83	$53.85	$53.80
Purchase #5	$163.59	9.571%	$179.2472	$179.25	$179.25	$179.20
Purchase #6	$159.53	4.295%	$166.3818	$166.38	$166.40	$166.40
Purchase #7	$209.85	7.751%	$226.1155	$226.12	$226.10	$226.10
7 purchase totals =	$899.23		$970.9688	$970.98	$971.00	$970.90