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	$136.63	6.384%	$145.3525	$145.35	$145.35	$145.40
Purchase #2	$100.51	7.305%	$107.8523	$107.85	$107.85	$107.90
Purchase #3	$16.25	7.502%	$17.4691	$17.47	$17.45	$17.50
Purchase #4	$92.71	10.256%	$102.2183	$102.22	$102.20	$102.20
Purchase #5	$205.84	13.643%	$233.9228	$233.92	$233.90	$233.90
Purchase #6	$118.86	10.752%	$131.6398	$131.64	$131.65	$131.60
Purchase #7	$78.59	4.410%	$82.0558	$82.06	$82.05	$82.10
7 purchase totals =	$749.39		$820.5106	$820.51	$820.45	$820.60