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	$246.70	6.671%	$263.1574	$263.16	$263.15	$263.20
Purchase #2	$131.97	8.189%	$142.777	$142.78	$142.80	$142.80
Purchase #3	$196.35	8.262%	$212.5724	$212.57	$212.55	$212.60
Purchase #4	$30.76	8.249%	$33.2974	$33.30	$33.30	$33.30
Purchase #5	$144.45	7.228%	$154.8908	$154.89	$154.90	$154.90
Purchase #6	$99.32	13.610%	$112.8375	$112.84	$112.85	$112.80
Purchase #7	$168.55	9.171%	$184.0077	$184.01	$184.00	$184.00
7 purchase totals =	$1,018.10		$1,103.5402	$1,103.55	$1,103.55	$1,103.60