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	$19.81	3.681%	$20.5392	$20.54	$20.55	$20.50
Purchase #2	$164.56	8.608%	$178.7253	$178.73	$178.75	$178.70
Purchase #3	$150.78	4.802%	$158.0205	$158.02	$158.00	$158.00
Purchase #4	$45.29	11.350%	$50.4304	$50.43	$50.45	$50.40
Purchase #5	$104.52	9.667%	$114.6239	$114.62	$114.60	$114.60
Purchase #6	$103.45	13.869%	$117.7975	$117.80	$117.80	$117.80
Purchase #7	$39.89	11.510%	$44.4813	$44.48	$44.50	$44.50
7 purchase totals =	$628.30		$684.6181	$684.62	$684.65	$684.50