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	$224.94	6.845%	$240.3371	$240.34	$240.35	$240.30
Purchase #2	$75.55	13.356%	$85.6405	$85.64	$85.65	$85.60
Purchase #3	$141.66	7.464%	$152.2335	$152.23	$152.25	$152.20
Purchase #4	$120.53	6.757%	$128.6742	$128.67	$128.65	$128.70
Purchase #5	$144.75	13.649%	$164.5069	$164.51	$164.50	$164.50
Purchase #6	$141.68	9.786%	$155.5448	$155.54	$155.55	$155.50
Purchase #7	$91.35	10.160%	$100.6312	$100.63	$100.65	$100.60
7 purchase totals =	$940.46		$1,027.5682	$1,027.56	$1,027.60	$1,027.40