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	$97.31	6.676%	$103.8064	$103.81	$103.80	$103.80
Purchase #2	$80.39	11.354%	$89.5175	$89.52	$89.50	$89.50
Purchase #3	$74.46	4.164%	$77.5605	$77.56	$77.55	$77.60
Purchase #4	$62.25	6.637%	$66.3815	$66.38	$66.40	$66.40
Purchase #5	$178.68	3.175%	$184.3531	$184.35	$184.35	$184.40
Purchase #6	$33.64	10.243%	$37.0857	$37.09	$37.10	$37.10
Purchase #7	$83.46	9.611%	$91.4813	$91.48	$91.50	$91.50
7 purchase totals =	$610.19		$650.1860	$650.19	$650.20	$650.30