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	$105.90	12.784%	$119.4383	$119.44	$119.45	$119.40
Purchase #2	$144.67	6.787%	$154.4888	$154.49	$154.50	$154.50
Purchase #3	$62.48	13.759%	$71.0766	$71.08	$71.10	$71.10
Purchase #4	$173.85	13.312%	$196.9929	$196.99	$197.00	$197.00
Purchase #5	$180.59	8.553%	$196.0359	$196.04	$196.05	$196.00
Purchase #6	$237.34	7.525%	$255.1998	$255.20	$255.20	$255.20
Purchase #7	$108.58	3.505%	$112.3857	$112.39	$112.40	$112.40
7 purchase totals =	$1,013.41		$1,105.6180	$1,105.63	$1,105.70	$1,105.60