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	$111.64	4.393%	$116.5443	$116.54	$116.55	$116.50
Purchase #2	$75.52	13.470%	$85.6925	$85.69	$85.70	$85.70
Purchase #3	$112.59	9.633%	$123.4358	$123.44	$123.45	$123.40
Purchase #4	$29.36	13.105%	$33.2076	$33.21	$33.20	$33.20
Purchase #5	$46.52	3.125%	$47.9738	$47.97	$47.95	$48.00
Purchase #6	$46.56	7.675%	$50.1335	$50.13	$50.15	$50.10
Purchase #7	$62.33	8.858%	$67.8512	$67.85	$67.85	$67.90
7 purchase totals =	$484.52		$524.8387	$524.83	$524.85	$524.80