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	$80.52	5.863%	$85.2409	$85.24	$85.25	$85.20
Purchase #2	$237.86	12.469%	$267.5188	$267.52	$267.50	$267.50
Purchase #3	$152.42	11.244%	$169.5581	$169.56	$169.55	$169.60
Purchase #4	$234.66	9.257%	$256.3825	$256.38	$256.40	$256.40
Purchase #5	$216.45	10.493%	$239.1621	$239.16	$239.15	$239.20
Purchase #6	$162.51	13.517%	$184.4765	$184.48	$184.50	$184.50
Purchase #7	$30.80	6.600%	$32.8328	$32.83	$32.85	$32.80
7 purchase totals =	$1,115.22		$1,235.1717	$1,235.17	$1,235.20	$1,235.20