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	$158.82	12.804%	$179.1553	$179.16	$179.15	$179.20
Purchase #2	$87.94	12.277%	$98.7364	$98.74	$98.75	$98.70
Purchase #3	$186.62	5.446%	$196.7833	$196.78	$196.80	$196.80
Purchase #4	$238.49	7.253%	$255.7877	$255.79	$255.80	$255.80
Purchase #5	$61.51	10.268%	$67.8258	$67.83	$67.85	$67.80
Purchase #6	$102.89	13.682%	$116.9674	$116.97	$116.95	$117.00
Purchase #7	$37.95	7.533%	$40.8088	$40.81	$40.80	$40.80
7 purchase totals =	$874.22		$956.0647	$956.08	$956.10	$956.10