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	$97.94	5.431%	$103.2591	$103.26	$103.25	$103.30
Purchase #2	$36.36	10.822%	$40.2949	$40.29	$40.30	$40.30
Purchase #3	$155.86	5.277%	$164.0847	$164.08	$164.10	$164.10
Purchase #4	$42.66	12.648%	$48.0556	$48.06	$48.05	$48.10
Purchase #5	$98.30	12.325%	$110.4155	$110.42	$110.40	$110.40
Purchase #6	$103.87	13.851%	$118.257	$118.26	$118.25	$118.30
Purchase #7	$30.91	8.249%	$33.4598	$33.46	$33.45	$33.50
7 purchase totals =	$565.90		$617.8266	$617.83	$617.80	$618.00