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	$101.65	12.602%	$114.4599	$114.46	$114.45	$114.50
Purchase #2	$206.45	7.593%	$222.1257	$222.13	$222.15	$222.10
Purchase #3	$171.69	9.491%	$187.9851	$187.99	$188.00	$188.00
Purchase #4	$166.69	4.703%	$174.5294	$174.53	$174.55	$174.50
Purchase #5	$196.93	10.411%	$217.4324	$217.43	$217.45	$217.40
Purchase #6	$86.31	4.527%	$90.2173	$90.22	$90.20	$90.20
Purchase #7	$121.50	8.188%	$131.4484	$131.45	$131.45	$131.40
7 purchase totals =	$1,051.22		$1,138.1982	$1,138.21	$1,138.25	$1,138.10