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	$37.38	13.515%	$42.4319	$42.43	$42.45	$42.40
Purchase #2	$35.61	8.679%	$38.7006	$38.70	$38.70	$38.70
Purchase #3	$186.67	5.104%	$196.1976	$196.20	$196.20	$196.20
Purchase #4	$161.75	6.350%	$172.0211	$172.02	$172.00	$172.00
Purchase #5	$95.35	7.455%	$102.4583	$102.46	$102.45	$102.50
Purchase #6	$198.66	5.148%	$208.887	$208.89	$208.90	$208.90
Purchase #7	$220.94	10.724%	$244.6336	$244.63	$244.65	$244.60
7 purchase totals =	$936.36		$1,005.3301	$1,005.33	$1,005.35	$1,005.30