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	$36.42	6.293%	$38.7119	$38.71	$38.70	$38.70
Purchase #2	$43.80	6.633%	$46.7053	$46.71	$46.70	$46.70
Purchase #3	$239.53	6.535%	$255.1833	$255.18	$255.20	$255.20
Purchase #4	$43.52	13.802%	$49.5266	$49.53	$49.55	$49.50
Purchase #5	$45.83	3.415%	$47.3951	$47.40	$47.40	$47.40
Purchase #6	$73.49	3.410%	$75.996	$76.00	$76.00	$76.00
Purchase #7	$178.51	10.311%	$196.9162	$196.92	$196.90	$196.90
7 purchase totals =	$661.10		$710.4344	$710.45	$710.45	$710.40