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	$129.69	6.216%	$137.7515	$137.75	$137.75	$137.80
Purchase #2	$80.72	7.752%	$86.9774	$86.98	$87.00	$87.00
Purchase #3	$27.59	8.316%	$29.8844	$29.88	$29.90	$29.90
Purchase #4	$250.29	6.801%	$267.3122	$267.31	$267.30	$267.30
Purchase #5	$56.57	12.420%	$63.596	$63.60	$63.60	$63.60
Purchase #6	$202.52	12.321%	$227.4725	$227.47	$227.45	$227.50
Purchase #7	$40.69	6.293%	$43.2506	$43.25	$43.25	$43.30
7 purchase totals =	$788.07		$856.2446	$856.24	$856.25	$856.40