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	$51.52	8.500%	$55.8992	$55.90	$55.90	$55.90
Purchase #2	$214.93	11.324%	$239.2687	$239.27	$239.25	$239.30
Purchase #3	$157.54	7.634%	$169.5666	$169.57	$169.55	$169.60
Purchase #4	$191.95	7.557%	$206.4557	$206.46	$206.45	$206.50
Purchase #5	$136.50	8.451%	$148.0356	$148.04	$148.05	$148.00
Purchase #6	$47.56	12.826%	$53.66	$53.66	$53.65	$53.70
Purchase #7	$131.61	9.708%	$144.3867	$144.39	$144.40	$144.40
7 purchase totals =	$931.61		$1,017.2725	$1,017.29	$1,017.25	$1,017.40