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	$97.37	7.214%	$104.3943	$104.39	$104.40	$104.40
Purchase #2	$134.60	7.351%	$144.4944	$144.49	$144.50	$144.50
Purchase #3	$68.53	6.222%	$72.7939	$72.79	$72.80	$72.80
Purchase #4	$64.49	13.112%	$72.9459	$72.95	$72.95	$72.90
Purchase #5	$54.60	3.734%	$56.6388	$56.64	$56.65	$56.60
Purchase #6	$38.99	3.549%	$40.3738	$40.37	$40.35	$40.40
Purchase #7	$141.37	9.417%	$154.6828	$154.68	$154.70	$154.70
7 purchase totals =	$599.95		$646.3239	$646.31	$646.35	$646.30