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	$51.78	11.736%	$57.8569	$57.86	$57.85	$57.90
Purchase #2	$105.82	7.264%	$113.5068	$113.51	$113.50	$113.50
Purchase #3	$217.54	9.443%	$238.0823	$238.08	$238.10	$238.10
Purchase #4	$244.71	4.231%	$255.0637	$255.06	$255.05	$255.10
Purchase #5	$198.90	13.228%	$225.2105	$225.21	$225.20	$225.20
Purchase #6	$135.38	13.603%	$153.7957	$153.80	$153.80	$153.80
Purchase #7	$213.85	12.469%	$240.515	$240.52	$240.50	$240.50
7 purchase totals =	$1,167.98		$1,284.0309	$1,284.04	$1,284.00	$1,284.10