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	$152.97	3.674%	$158.5901	$158.59	$158.60	$158.60
Purchase #2	$145.34	6.213%	$154.37	$154.37	$154.35	$154.40
Purchase #3	$160.94	3.526%	$166.6147	$166.61	$166.60	$166.60
Purchase #4	$164.66	13.521%	$186.9237	$186.92	$186.90	$186.90
Purchase #5	$17.26	13.481%	$19.5868	$19.59	$19.60	$19.60
Purchase #6	$191.25	10.780%	$211.8668	$211.87	$211.85	$211.90
Purchase #7	$69.66	13.267%	$78.9018	$78.90	$78.90	$78.90
7 purchase totals =	$902.08		$976.8539	$976.85	$976.80	$976.90