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	$229.43	5.438%	$241.9064	$241.91	$241.90	$241.90
Purchase #2	$190.50	13.334%	$215.9013	$215.90	$215.90	$215.90
Purchase #3	$57.79	13.369%	$65.5159	$65.52	$65.50	$65.50
Purchase #4	$24.71	12.212%	$27.7276	$27.73	$27.75	$27.70
Purchase #5	$123.97	8.583%	$134.6103	$134.61	$134.60	$134.60
Purchase #6	$26.63	12.709%	$30.0144	$30.01	$30.00	$30.00
Purchase #7	$72.35	13.688%	$82.2533	$82.25	$82.25	$82.30
7 purchase totals =	$725.38		$797.9292	$797.93	$797.90	$797.90