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	$28.27	11.756%	$31.5934	$31.59	$31.60	$31.60
Purchase #2	$185.42	7.260%	$198.8815	$198.88	$198.90	$198.90
Purchase #3	$164.80	13.845%	$187.6166	$187.62	$187.60	$187.60
Purchase #4	$37.70	13.723%	$42.8736	$42.87	$42.85	$42.90
Purchase #5	$129.44	11.611%	$144.4693	$144.47	$144.45	$144.50
Purchase #6	$14.78	12.540%	$16.6334	$16.63	$16.65	$16.60
Purchase #7	$90.74	12.775%	$102.332	$102.33	$102.35	$102.30
7 purchase totals =	$651.15		$724.3998	$724.39	$724.40	$724.40