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	$74.31	5.293%	$78.2432	$78.24	$78.25	$78.20
Purchase #2	$241.82	5.797%	$255.8383	$255.84	$255.85	$255.80
Purchase #3	$122.84	7.515%	$132.0714	$132.07	$132.05	$132.10
Purchase #4	$136.30	5.143%	$143.3099	$143.31	$143.30	$143.30
Purchase #5	$141.82	9.253%	$154.9426	$154.94	$154.95	$154.90
Purchase #6	$215.26	12.243%	$241.6143	$241.61	$241.60	$241.60
Purchase #7	$231.52	13.390%	$262.5205	$262.52	$262.50	$262.50
7 purchase totals =	$1,163.87		$1,268.5402	$1,268.53	$1,268.50	$1,268.40