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	$248.93	12.754%	$280.6785	$280.68	$280.70	$280.70
Purchase #2	$95.78	11.755%	$107.0389	$107.04	$107.05	$107.00
Purchase #3	$128.28	10.864%	$142.2163	$142.22	$142.20	$142.20
Purchase #4	$227.30	12.425%	$255.542	$255.54	$255.55	$255.50
Purchase #5	$176.30	11.691%	$196.9112	$196.91	$196.90	$196.90
Purchase #6	$102.71	13.177%	$116.2441	$116.24	$116.25	$116.20
Purchase #7	$62.54	10.539%	$69.1311	$69.13	$69.15	$69.10
7 purchase totals =	$1,041.84		$1,167.7621	$1,167.76	$1,167.80	$1,167.60