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	$69.51	13.149%	$78.6499	$78.65	$78.65	$78.60
Purchase #2	$78.70	3.241%	$81.2507	$81.25	$81.25	$81.30
Purchase #3	$223.78	13.625%	$254.27	$254.27	$254.25	$254.30
Purchase #4	$29.39	7.523%	$31.601	$31.60	$31.60	$31.60
Purchase #5	$137.57	5.871%	$145.6467	$145.65	$145.65	$145.60
Purchase #6	$160.34	5.611%	$169.3367	$169.34	$169.35	$169.30
Purchase #7	$17.66	5.634%	$18.655	$18.66	$18.65	$18.70
7 purchase totals =	$716.95		$779.4100	$779.42	$779.40	$779.40