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	$20.71	10.395%	$22.8628	$22.86	$22.85	$22.90
Purchase #2	$141.86	7.528%	$152.5392	$152.54	$152.55	$152.50
Purchase #3	$132.76	4.543%	$138.7913	$138.79	$138.80	$138.80
Purchase #4	$40.54	7.548%	$43.6	$43.60	$43.60	$43.60
Purchase #5	$6.92	8.136%	$7.483	$7.48	$7.50	$7.50
Purchase #6	$50.95	5.834%	$53.9224	$53.92	$53.90	$53.90
Purchase #7	$162.81	3.151%	$167.9401	$167.94	$167.95	$167.90
7 purchase totals =	$556.55		$587.1388	$587.13	$587.15	$587.10