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	$80.32	11.806%	$89.8026	$89.80	$89.80	$89.80
Purchase #2	$105.51	5.851%	$111.6834	$111.68	$111.70	$111.70
Purchase #3	$121.40	10.286%	$133.8872	$133.89	$133.90	$133.90
Purchase #4	$156.33	4.567%	$163.4696	$163.47	$163.45	$163.50
Purchase #5	$102.40	11.233%	$113.9026	$113.90	$113.90	$113.90
Purchase #6	$21.40	13.836%	$24.3609	$24.36	$24.35	$24.40
Purchase #7	$61.67	12.391%	$69.3115	$69.31	$69.30	$69.30
7 purchase totals =	$649.03		$706.4178	$706.41	$706.40	$706.50