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	$137.40	8.590%	$149.2027	$149.20	$149.20	$149.20
Purchase #2	$40.79	6.657%	$43.5054	$43.51	$43.50	$43.50
Purchase #3	$209.42	13.713%	$238.1378	$238.14	$238.15	$238.10
Purchase #4	$104.32	9.181%	$113.8976	$113.90	$113.90	$113.90
Purchase #5	$90.82	12.592%	$102.2561	$102.26	$102.25	$102.30
Purchase #6	$153.33	3.557%	$158.7839	$158.78	$158.80	$158.80
Purchase #7	$123.81	11.161%	$137.6284	$137.63	$137.65	$137.60
7 purchase totals =	$859.89		$943.4119	$943.42	$943.45	$943.40