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	$129.55	11.650%	$144.6426	$144.64	$144.65	$144.60
Purchase #2	$85.40	7.236%	$91.5795	$91.58	$91.60	$91.60
Purchase #3	$93.39	11.774%	$104.3857	$104.39	$104.40	$104.40
Purchase #4	$247.64	9.266%	$270.5863	$270.59	$270.60	$270.60
Purchase #5	$72.31	11.720%	$80.7847	$80.78	$80.80	$80.80
Purchase #6	$75.90	3.126%	$78.2726	$78.27	$78.25	$78.30
Purchase #7	$202.48	13.726%	$230.2724	$230.27	$230.25	$230.30
7 purchase totals =	$906.67		$1,000.5238	$1,000.52	$1,000.55	$1,000.60