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	$52.28	5.357%	$55.0806	$55.08	$55.10	$55.10
Purchase #2	$184.96	6.168%	$196.3683	$196.37	$196.35	$196.40
Purchase #3	$140.49	12.593%	$158.1819	$158.18	$158.20	$158.20
Purchase #4	$82.99	7.318%	$89.0632	$89.06	$89.05	$89.10
Purchase #5	$81.38	10.610%	$90.0144	$90.01	$90.00	$90.00
Purchase #6	$141.27	10.547%	$156.1697	$156.17	$156.15	$156.20
Purchase #7	$136.47	3.786%	$141.6368	$141.64	$141.65	$141.60
7 purchase totals =	$819.84		$886.5149	$886.51	$886.50	$886.60