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	$53.93	6.484%	$57.4268	$57.43	$57.45	$57.40
Purchase #2	$146.28	13.500%	$166.0278	$166.03	$166.05	$166.00
Purchase #3	$123.90	6.379%	$131.8036	$131.80	$131.80	$131.80
Purchase #4	$217.89	11.345%	$242.6096	$242.61	$242.60	$242.60
Purchase #5	$43.98	10.194%	$48.4633	$48.46	$48.45	$48.50
Purchase #6	$178.39	4.480%	$186.3819	$186.38	$186.40	$186.40
Purchase #7	$231.90	6.805%	$247.6808	$247.68	$247.70	$247.70
7 purchase totals =	$996.27		$1,080.3938	$1,080.39	$1,080.45	$1,080.40