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	$133.40	4.860%	$139.8832	$139.88	$139.90	$139.90
Purchase #2	$187.82	13.526%	$213.2245	$213.22	$213.20	$213.20
Purchase #3	$40.95	5.332%	$43.1335	$43.13	$43.15	$43.10
Purchase #4	$212.56	12.293%	$238.69	$238.69	$238.70	$238.70
Purchase #5	$13.95	11.321%	$15.5293	$15.53	$15.55	$15.50
Purchase #6	$191.39	3.754%	$198.5748	$198.57	$198.55	$198.60
Purchase #7	$224.61	6.181%	$238.4931	$238.49	$238.50	$238.50
7 purchase totals =	$1,004.68		$1,087.5284	$1,087.51	$1,087.55	$1,087.50