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	$6.51	12.382%	$7.3161	$7.32	$7.30	$7.30
Purchase #2	$107.44	10.230%	$118.4311	$118.43	$118.45	$118.40
Purchase #3	$30.64	6.474%	$32.6236	$32.62	$32.60	$32.60
Purchase #4	$226.43	13.372%	$256.7082	$256.71	$256.70	$256.70
Purchase #5	$247.49	10.360%	$273.13	$273.13	$273.15	$273.10
Purchase #6	$157.65	4.296%	$164.4226	$164.42	$164.40	$164.40
Purchase #7	$33.86	12.666%	$38.1487	$38.15	$38.15	$38.10
7 purchase totals =	$810.02		$890.7803	$890.78	$890.75	$890.60