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	$52.68	5.449%	$55.5505	$55.55	$55.55	$55.60
Purchase #2	$33.52	13.195%	$37.943	$37.94	$37.95	$37.90
Purchase #3	$148.84	12.840%	$167.9511	$167.95	$167.95	$168.00
Purchase #4	$126.34	12.638%	$142.3068	$142.31	$142.30	$142.30
Purchase #5	$166.31	8.474%	$180.4031	$180.40	$180.40	$180.40
Purchase #6	$172.78	9.136%	$188.5652	$188.57	$188.55	$188.60
Purchase #7	$55.96	7.834%	$60.3439	$60.34	$60.35	$60.30
7 purchase totals =	$756.43		$833.0636	$833.06	$833.05	$833.10