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	$223.31	5.405%	$235.3799	$235.38	$235.40	$235.40
Purchase #2	$82.70	8.638%	$89.8436	$89.84	$89.85	$89.80
Purchase #3	$163.68	13.348%	$185.528	$185.53	$185.55	$185.50
Purchase #4	$115.78	9.362%	$126.6193	$126.62	$126.60	$126.60
Purchase #5	$56.93	10.561%	$62.9424	$62.94	$62.95	$62.90
Purchase #6	$15.82	11.261%	$17.6015	$17.60	$17.60	$17.60
Purchase #7	$199.86	6.823%	$213.4964	$213.50	$213.50	$213.50
7 purchase totals =	$858.08		$931.4111	$931.41	$931.45	$931.30