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	$135.34	7.695%	$145.7544	$145.75	$145.75	$145.80
Purchase #2	$39.97	6.156%	$42.4306	$42.43	$42.45	$42.40
Purchase #3	$176.32	7.540%	$189.6145	$189.61	$189.60	$189.60
Purchase #4	$38.47	7.616%	$41.3999	$41.40	$41.40	$41.40
Purchase #5	$125.92	12.869%	$142.1246	$142.12	$142.10	$142.10
Purchase #6	$144.64	10.683%	$160.0919	$160.09	$160.10	$160.10
Purchase #7	$65.51	4.590%	$68.5169	$68.52	$68.50	$68.50
7 purchase totals =	$726.17		$789.9328	$789.92	$789.90	$789.90