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	$30.49	6.599%	$32.502	$32.50	$32.50	$32.50
Purchase #2	$218.55	10.588%	$241.6901	$241.69	$241.70	$241.70
Purchase #3	$162.85	12.246%	$182.7926	$182.79	$182.80	$182.80
Purchase #4	$25.81	5.735%	$27.2902	$27.29	$27.30	$27.30
Purchase #5	$62.90	5.528%	$66.3771	$66.38	$66.40	$66.40
Purchase #6	$75.37	9.334%	$82.405	$82.41	$82.40	$82.40
Purchase #7	$77.81	12.458%	$87.5036	$87.50	$87.50	$87.50
7 purchase totals =	$653.78		$720.5606	$720.56	$720.60	$720.60