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	$42.45	7.533%	$45.6478	$45.65	$45.65	$45.60
Purchase #2	$96.85	11.332%	$107.825	$107.83	$107.85	$107.80
Purchase #3	$150.76	3.827%	$156.5296	$156.53	$156.55	$156.50
Purchase #4	$113.52	6.770%	$121.2053	$121.21	$121.20	$121.20
Purchase #5	$82.85	9.399%	$90.6371	$90.64	$90.65	$90.60
Purchase #6	$230.50	12.595%	$259.5315	$259.53	$259.55	$259.50
Purchase #7	$66.46	5.378%	$70.0342	$70.03	$70.05	$70.00
7 purchase totals =	$783.39		$851.4105	$851.42	$851.50	$851.20