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	$38.50	3.738%	$39.9391	$39.94	$39.95	$39.90
Purchase #2	$38.28	9.136%	$41.7773	$41.78	$41.80	$41.80
Purchase #3	$231.83	7.601%	$249.4514	$249.45	$249.45	$249.50
Purchase #4	$162.69	13.155%	$184.0919	$184.09	$184.10	$184.10
Purchase #5	$172.42	7.112%	$184.6825	$184.68	$184.70	$184.70
Purchase #6	$68.83	11.609%	$76.8205	$76.82	$76.80	$76.80
Purchase #7	$247.28	13.487%	$280.6307	$280.63	$280.65	$280.60
7 purchase totals =	$959.83		$1,057.3934	$1,057.39	$1,057.45	$1,057.40