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	$210.87	9.680%	$231.2822	$231.28	$231.30	$231.30
Purchase #2	$196.74	6.538%	$209.6029	$209.60	$209.60	$209.60
Purchase #3	$235.64	8.821%	$256.4258	$256.43	$256.45	$256.40
Purchase #4	$142.66	5.626%	$150.6861	$150.69	$150.70	$150.70
Purchase #5	$84.60	4.341%	$88.2725	$88.27	$88.25	$88.30
Purchase #6	$179.72	7.162%	$192.5915	$192.59	$192.60	$192.60
Purchase #7	$116.94	12.279%	$131.2991	$131.30	$131.30	$131.30
7 purchase totals =	$1,167.17		$1,260.1601	$1,260.16	$1,260.20	$1,260.20