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	$34.92	11.732%	$39.0168	$39.02	$39.00	$39.00
Purchase #2	$190.75	9.754%	$209.3558	$209.36	$209.35	$209.40
Purchase #3	$136.93	5.602%	$144.6008	$144.60	$144.60	$144.60
Purchase #4	$113.50	11.328%	$126.3573	$126.36	$126.35	$126.40
Purchase #5	$140.34	4.272%	$146.3353	$146.34	$146.35	$146.30
Purchase #6	$247.92	13.567%	$281.5553	$281.56	$281.55	$281.60
Purchase #7	$181.90	8.127%	$196.683	$196.68	$196.70	$196.70
7 purchase totals =	$1,046.26		$1,143.9043	$1,143.92	$1,143.90	$1,144.00