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	$8.63	11.364%	$9.6107	$9.61	$9.60	$9.60
Purchase #2	$116.92	6.686%	$124.7373	$124.74	$124.75	$124.70
Purchase #3	$114.48	11.527%	$127.6761	$127.68	$127.70	$127.70
Purchase #4	$160.68	3.313%	$166.0033	$166.00	$166.00	$166.00
Purchase #5	$127.45	3.485%	$131.8916	$131.89	$131.90	$131.90
Purchase #6	$40.82	3.874%	$42.4014	$42.40	$42.40	$42.40
Purchase #7	$228.65	13.492%	$259.4995	$259.50	$259.50	$259.50
7 purchase totals =	$797.63		$861.8199	$861.82	$861.85	$861.80