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	$17.78	3.581%	$18.4167	$18.42	$18.40	$18.40
Purchase #2	$164.73	9.154%	$179.8094	$179.81	$179.80	$179.80
Purchase #3	$164.78	10.455%	$182.0077	$182.01	$182.00	$182.00
Purchase #4	$192.29	7.389%	$206.4983	$206.50	$206.50	$206.50
Purchase #5	$226.70	3.385%	$234.3738	$234.37	$234.35	$234.40
Purchase #6	$167.29	10.188%	$184.3335	$184.33	$184.35	$184.30
Purchase #7	$27.66	13.686%	$31.4455	$31.45	$31.45	$31.40
7 purchase totals =	$961.23		$1,036.8849	$1,036.89	$1,036.85	$1,036.80