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	$122.60	4.857%	$128.5547	$128.55	$128.55	$128.60
Purchase #2	$86.67	4.342%	$90.4332	$90.43	$90.45	$90.40
Purchase #3	$88.44	12.425%	$99.4287	$99.43	$99.45	$99.40
Purchase #4	$156.45	3.849%	$162.4718	$162.47	$162.45	$162.50
Purchase #5	$102.43	13.372%	$116.1269	$116.13	$116.15	$116.10
Purchase #6	$99.91	8.301%	$108.2035	$108.20	$108.20	$108.20
Purchase #7	$156.76	3.591%	$162.3893	$162.39	$162.40	$162.40
7 purchase totals =	$813.26		$867.6081	$867.60	$867.65	$867.60