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	$97.77	10.617%	$108.1502	$108.15	$108.15	$108.20
Purchase #2	$133.78	9.770%	$146.8503	$146.85	$146.85	$146.90
Purchase #3	$134.44	3.863%	$139.6334	$139.63	$139.65	$139.60
Purchase #4	$80.66	12.702%	$90.9054	$90.91	$90.90	$90.90
Purchase #5	$153.39	7.498%	$164.8912	$164.89	$164.90	$164.90
Purchase #6	$5.92	10.556%	$6.5449	$6.54	$6.55	$6.50
Purchase #7	$131.72	13.261%	$149.1874	$149.19	$149.20	$149.20
7 purchase totals =	$737.68		$806.1628	$806.16	$806.20	$806.20