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	$49.69	3.824%	$51.5901	$51.59	$51.60	$51.60
Purchase #2	$99.90	4.533%	$104.4285	$104.43	$104.45	$104.40
Purchase #3	$244.30	13.828%	$278.0818	$278.08	$278.10	$278.10
Purchase #4	$157.32	4.290%	$164.069	$164.07	$164.05	$164.10
Purchase #5	$18.47	3.448%	$19.1068	$19.11	$19.10	$19.10
Purchase #6	$30.90	13.400%	$35.0406	$35.04	$35.05	$35.00
Purchase #7	$118.77	10.561%	$131.3133	$131.31	$131.30	$131.30
7 purchase totals =	$719.35		$783.6301	$783.63	$783.65	$783.60