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	$86.31	3.276%	$89.1375	$89.14	$89.15	$89.10
Purchase #2	$118.39	6.343%	$125.8995	$125.90	$125.90	$125.90
Purchase #3	$81.77	8.683%	$88.8701	$88.87	$88.85	$88.90
Purchase #4	$157.75	5.666%	$166.6881	$166.69	$166.70	$166.70
Purchase #5	$46.56	12.671%	$52.4596	$52.46	$52.45	$52.50
Purchase #6	$189.38	11.380%	$210.9314	$210.93	$210.95	$210.90
Purchase #7	$225.55	13.746%	$256.5541	$256.55	$256.55	$256.60
7 purchase totals =	$905.71		$990.5403	$990.54	$990.55	$990.60