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	$230.86	12.613%	$259.9784	$259.98	$260.00	$260.00
Purchase #2	$112.64	12.229%	$126.4147	$126.41	$126.40	$126.40
Purchase #3	$131.82	10.663%	$145.876	$145.88	$145.90	$145.90
Purchase #4	$38.75	10.637%	$42.8718	$42.87	$42.85	$42.90
Purchase #5	$88.42	9.242%	$96.5918	$96.59	$96.60	$96.60
Purchase #6	$217.43	6.653%	$231.8956	$231.90	$231.90	$231.90
Purchase #7	$237.29	12.705%	$267.4377	$267.44	$267.45	$267.40
7 purchase totals =	$1,057.21		$1,171.0660	$1,171.07	$1,171.10	$1,171.10