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	$246.51	3.763%	$255.7862	$255.79	$255.80	$255.80
Purchase #2	$38.57	11.755%	$43.1039	$43.10	$43.10	$43.10
Purchase #3	$34.49	11.782%	$38.5536	$38.55	$38.55	$38.60
Purchase #4	$201.41	10.654%	$222.8682	$222.87	$222.85	$222.90
Purchase #5	$195.77	7.559%	$210.5683	$210.57	$210.55	$210.60
Purchase #6	$72.50	10.834%	$80.3547	$80.35	$80.35	$80.40
Purchase #7	$208.94	7.397%	$224.3953	$224.40	$224.40	$224.40
7 purchase totals =	$998.19		$1,075.6302	$1,075.63	$1,075.60	$1,075.80