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	$243.46	13.704%	$276.8238	$276.82	$276.80	$276.80
Purchase #2	$144.82	9.615%	$158.7444	$158.74	$158.75	$158.70
Purchase #3	$241.48	7.443%	$259.4534	$259.45	$259.45	$259.50
Purchase #4	$141.96	11.655%	$158.5054	$158.51	$158.50	$158.50
Purchase #5	$77.81	10.124%	$85.6875	$85.69	$85.70	$85.70
Purchase #6	$156.26	12.193%	$175.3128	$175.31	$175.30	$175.30
Purchase #7	$201.35	10.295%	$222.079	$222.08	$222.10	$222.10
7 purchase totals =	$1,207.14		$1,336.6063	$1,336.60	$1,336.60	$1,336.60