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	$88.90	4.762%	$93.1334	$93.13	$93.15	$93.10
Purchase #2	$249.27	12.182%	$279.6361	$279.64	$279.65	$279.60
Purchase #3	$68.97	5.139%	$72.5144	$72.51	$72.50	$72.50
Purchase #4	$7.30	3.270%	$7.5387	$7.54	$7.55	$7.50
Purchase #5	$52.53	3.738%	$54.4936	$54.49	$54.50	$54.50
Purchase #6	$38.61	3.495%	$39.9594	$39.96	$39.95	$40.00
Purchase #7	$50.86	5.774%	$53.7967	$53.80	$53.80	$53.80
7 purchase totals =	$556.44		$601.0723	$601.07	$601.10	$601.00