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	$19.37	10.436%	$21.3915	$21.39	$21.40	$21.40
Purchase #2	$115.45	10.438%	$127.5007	$127.50	$127.50	$127.50
Purchase #3	$111.39	6.254%	$118.3563	$118.36	$118.35	$118.40
Purchase #4	$155.85	3.506%	$161.3141	$161.31	$161.30	$161.30
Purchase #5	$231.69	9.132%	$252.8479	$252.85	$252.85	$252.80
Purchase #6	$39.83	9.798%	$43.7325	$43.73	$43.75	$43.70
Purchase #7	$177.96	10.433%	$196.5266	$196.53	$196.55	$196.50
7 purchase totals =	$851.54		$921.6696	$921.67	$921.70	$921.60