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	$213.59	13.737%	$242.9309	$242.93	$242.95	$242.90
Purchase #2	$40.97	10.556%	$45.2948	$45.29	$45.30	$45.30
Purchase #3	$108.35	13.814%	$123.3175	$123.32	$123.30	$123.30
Purchase #4	$238.90	6.159%	$253.6139	$253.61	$253.60	$253.60
Purchase #5	$98.78	9.614%	$108.2767	$108.28	$108.30	$108.30
Purchase #6	$198.95	3.455%	$205.8237	$205.82	$205.80	$205.80
Purchase #7	$212.40	13.212%	$240.4623	$240.46	$240.45	$240.50
7 purchase totals =	$1,111.94		$1,219.7198	$1,219.71	$1,219.70	$1,219.70