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	$38.38	5.379%	$40.4445	$40.44	$40.45	$40.40
Purchase #2	$78.75	3.617%	$81.5984	$81.60	$81.60	$81.60
Purchase #3	$204.40	12.157%	$229.2489	$229.25	$229.25	$229.20
Purchase #4	$163.92	9.500%	$179.4924	$179.49	$179.50	$179.50
Purchase #5	$169.71	12.206%	$190.4248	$190.42	$190.40	$190.40
Purchase #6	$116.72	6.605%	$124.4294	$124.43	$124.45	$124.40
Purchase #7	$33.43	6.750%	$35.6865	$35.69	$35.70	$35.70
7 purchase totals =	$805.31		$881.3249	$881.32	$881.35	$881.20