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	$115.75	13.372%	$131.2281	$131.23	$131.25	$131.20
Purchase #2	$128.61	9.674%	$141.0517	$141.05	$141.05	$141.10
Purchase #3	$136.64	6.548%	$145.5872	$145.59	$145.60	$145.60
Purchase #4	$121.82	12.566%	$137.1279	$137.13	$137.15	$137.10
Purchase #5	$81.40	5.509%	$85.8843	$85.88	$85.90	$85.90
Purchase #6	$159.56	10.233%	$175.8878	$175.89	$175.90	$175.90
Purchase #7	$176.74	13.440%	$200.4939	$200.49	$200.50	$200.50
7 purchase totals =	$920.52		$1,017.2609	$1,017.26	$1,017.35	$1,017.30