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	$201.75	10.175%	$222.2781	$222.28	$222.30	$222.30
Purchase #2	$123.61	13.121%	$139.8289	$139.83	$139.85	$139.80
Purchase #3	$154.64	6.291%	$164.3684	$164.37	$164.35	$164.40
Purchase #4	$186.92	11.525%	$208.4625	$208.46	$208.45	$208.50
Purchase #5	$150.63	5.687%	$159.1963	$159.20	$159.20	$159.20
Purchase #6	$247.63	13.270%	$280.4905	$280.49	$280.50	$280.50
Purchase #7	$224.32	8.169%	$242.6447	$242.64	$242.65	$242.60
7 purchase totals =	$1,289.50		$1,417.2694	$1,417.27	$1,417.30	$1,417.30