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	$181.66	3.205%	$187.4822	$187.48	$187.50	$187.50
Purchase #2	$24.82	11.235%	$27.6085	$27.61	$27.60	$27.60
Purchase #3	$32.92	9.714%	$36.1178	$36.12	$36.10	$36.10
Purchase #4	$233.70	10.390%	$257.9814	$257.98	$258.00	$258.00
Purchase #5	$55.96	5.828%	$59.2213	$59.22	$59.20	$59.20
Purchase #6	$164.37	9.463%	$179.9243	$179.92	$179.90	$179.90
Purchase #7	$96.48	13.839%	$109.8319	$109.83	$109.85	$109.80
7 purchase totals =	$789.91		$858.1674	$858.16	$858.15	$858.10