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	$122.35	12.318%	$137.4211	$137.42	$137.40	$137.40
Purchase #2	$154.42	3.143%	$159.2734	$159.27	$159.25	$159.30
Purchase #3	$217.35	6.452%	$231.3734	$231.37	$231.35	$231.40
Purchase #4	$46.61	10.432%	$51.4724	$51.47	$51.45	$51.50
Purchase #5	$29.73	13.863%	$33.8515	$33.85	$33.85	$33.90
Purchase #6	$223.54	7.508%	$240.3234	$240.32	$240.30	$240.30
Purchase #7	$205.48	12.706%	$231.5883	$231.59	$231.60	$231.60
7 purchase totals =	$999.48		$1,085.3035	$1,085.29	$1,085.20	$1,085.40