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	$229.55	9.732%	$251.8898	$251.89	$251.90	$251.90
Purchase #2	$132.94	6.102%	$141.052	$141.05	$141.05	$141.10
Purchase #3	$178.87	11.859%	$200.0822	$200.08	$200.10	$200.10
Purchase #4	$100.50	10.337%	$110.8887	$110.89	$110.90	$110.90
Purchase #5	$155.59	13.646%	$176.8218	$176.82	$176.80	$176.80
Purchase #6	$43.68	7.381%	$46.904	$46.90	$46.90	$46.90
Purchase #7	$216.59	12.851%	$244.424	$244.42	$244.40	$244.40
7 purchase totals =	$1,057.72		$1,172.0625	$1,172.05	$1,172.05	$1,172.10