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	$131.43	8.176%	$142.1757	$142.18	$142.20	$142.20
Purchase #2	$99.57	13.721%	$113.232	$113.23	$113.25	$113.20
Purchase #3	$44.69	6.392%	$47.5466	$47.55	$47.55	$47.50
Purchase #4	$248.96	4.769%	$260.8329	$260.83	$260.85	$260.80
Purchase #5	$231.27	13.352%	$262.1492	$262.15	$262.15	$262.10
Purchase #6	$79.62	12.276%	$89.3942	$89.39	$89.40	$89.40
Purchase #7	$164.54	4.548%	$172.0233	$172.02	$172.00	$172.00
7 purchase totals =	$1,000.08		$1,087.3539	$1,087.35	$1,087.40	$1,087.20