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	$110.53	5.767%	$116.9043	$116.90	$116.90	$116.90
Purchase #2	$148.60	4.250%	$154.9155	$154.92	$154.90	$154.90
Purchase #3	$249.64	9.130%	$272.4321	$272.43	$272.45	$272.40
Purchase #4	$85.94	9.651%	$94.2341	$94.23	$94.25	$94.20
Purchase #5	$72.66	13.380%	$82.3819	$82.38	$82.40	$82.40
Purchase #6	$17.61	10.691%	$19.4927	$19.49	$19.50	$19.50
Purchase #7	$164.84	6.539%	$175.6189	$175.62	$175.60	$175.60
7 purchase totals =	$849.82		$915.9795	$915.97	$916.00	$915.90