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	$45.30	9.105%	$49.4246	$49.42	$49.40	$49.40
Purchase #2	$47.78	13.566%	$54.2618	$54.26	$54.25	$54.30
Purchase #3	$136.45	13.146%	$154.3877	$154.39	$154.40	$154.40
Purchase #4	$196.27	5.235%	$206.5447	$206.54	$206.55	$206.50
Purchase #5	$175.55	5.666%	$185.4967	$185.50	$185.50	$185.50
Purchase #6	$201.94	3.816%	$209.646	$209.65	$209.65	$209.60
Purchase #7	$166.80	7.522%	$179.3467	$179.35	$179.35	$179.30
7 purchase totals =	$970.09		$1,039.1082	$1,039.11	$1,039.10	$1,039.00