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	$107.60	4.574%	$112.5216	$112.52	$112.50	$112.50
Purchase #2	$152.35	11.267%	$169.5153	$169.52	$169.50	$169.50
Purchase #3	$216.67	10.464%	$239.3423	$239.34	$239.35	$239.30
Purchase #4	$198.51	4.866%	$208.1695	$208.17	$208.15	$208.20
Purchase #5	$156.58	6.852%	$167.3089	$167.31	$167.30	$167.30
Purchase #6	$77.29	6.476%	$82.2953	$82.30	$82.30	$82.30
Purchase #7	$16.84	9.538%	$18.4462	$18.45	$18.45	$18.40
7 purchase totals =	$925.84		$997.5991	$997.61	$997.55	$997.50