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	$82.92	9.566%	$90.8521	$90.85	$90.85	$90.90
Purchase #2	$177.71	6.729%	$189.6681	$189.67	$189.65	$189.70
Purchase #3	$153.81	3.821%	$159.6871	$159.69	$159.70	$159.70
Purchase #4	$71.83	13.606%	$81.6032	$81.60	$81.60	$81.60
Purchase #5	$95.88	9.349%	$104.8438	$104.84	$104.85	$104.80
Purchase #6	$213.85	3.524%	$221.3861	$221.39	$221.40	$221.40
Purchase #7	$46.59	8.518%	$50.5585	$50.56	$50.55	$50.60
7 purchase totals =	$842.59		$898.5989	$898.60	$898.60	$898.70