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	$72.77	12.732%	$82.0351	$82.04	$82.05	$82.00
Purchase #2	$108.87	6.863%	$116.3417	$116.34	$116.35	$116.30
Purchase #3	$118.95	10.468%	$131.4017	$131.40	$131.40	$131.40
Purchase #4	$131.29	9.429%	$143.6693	$143.67	$143.65	$143.70
Purchase #5	$37.57	4.858%	$39.3952	$39.40	$39.40	$39.40
Purchase #6	$170.43	5.222%	$179.3299	$179.33	$179.35	$179.30
Purchase #7	$24.49	11.190%	$27.2304	$27.23	$27.25	$27.20
7 purchase totals =	$664.37		$719.4033	$719.41	$719.45	$719.30