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	$163.30	4.366%	$170.4297	$170.43	$170.45	$170.40
Purchase #2	$108.89	4.315%	$113.5886	$113.59	$113.60	$113.60
Purchase #3	$207.32	13.699%	$235.7208	$235.72	$235.70	$235.70
Purchase #4	$144.64	11.321%	$161.0147	$161.01	$161.00	$161.00
Purchase #5	$131.57	12.567%	$148.1044	$148.10	$148.10	$148.10
Purchase #6	$100.87	10.504%	$111.4654	$111.47	$111.45	$111.50
Purchase #7	$88.97	12.412%	$100.013	$100.01	$100.00	$100.00
7 purchase totals =	$945.56		$1,040.3366	$1,040.33	$1,040.30	$1,040.30