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	$140.93	12.707%	$158.838	$158.84	$158.85	$158.80
Purchase #2	$160.86	13.697%	$182.893	$182.89	$182.90	$182.90
Purchase #3	$234.50	3.732%	$243.2515	$243.25	$243.25	$243.30
Purchase #4	$59.51	4.182%	$61.9987	$62.00	$62.00	$62.00
Purchase #5	$107.86	10.227%	$118.8908	$118.89	$118.90	$118.90
Purchase #6	$45.33	12.190%	$50.8557	$50.86	$50.85	$50.90
Purchase #7	$117.95	12.664%	$132.8872	$132.89	$132.90	$132.90
7 purchase totals =	$866.94		$949.6149	$949.62	$949.65	$949.70