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	$6.72	12.671%	$7.5715	$7.57	$7.55	$7.60
Purchase #2	$213.28	10.114%	$234.8511	$234.85	$234.85	$234.90
Purchase #3	$97.30	11.551%	$108.5391	$108.54	$108.55	$108.50
Purchase #4	$118.67	8.605%	$128.8816	$128.88	$128.90	$128.90
Purchase #5	$129.34	8.702%	$140.5952	$140.60	$140.60	$140.60
Purchase #6	$49.69	9.611%	$54.4657	$54.47	$54.45	$54.50
Purchase #7	$173.34	9.666%	$190.095	$190.10	$190.10	$190.10
7 purchase totals =	$788.34		$864.9992	$865.01	$865.00	$865.10