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	$133.81	4.402%	$139.7003	$139.70	$139.70	$139.70
Purchase #2	$189.46	12.373%	$212.9019	$212.90	$212.90	$212.90
Purchase #3	$108.88	7.356%	$116.8892	$116.89	$116.90	$116.90
Purchase #4	$141.25	10.784%	$156.4824	$156.48	$156.50	$156.50
Purchase #5	$18.28	10.536%	$20.206	$20.21	$20.20	$20.20
Purchase #6	$72.42	7.817%	$78.0811	$78.08	$78.10	$78.10
Purchase #7	$212.93	13.481%	$241.6351	$241.64	$241.65	$241.60
7 purchase totals =	$877.03		$965.8960	$965.90	$965.95	$965.90