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	$239.94	9.155%	$261.9065	$261.91	$261.90	$261.90
Purchase #2	$123.63	3.117%	$127.4835	$127.48	$127.50	$127.50
Purchase #3	$225.55	12.583%	$253.931	$253.93	$253.95	$253.90
Purchase #4	$247.52	13.191%	$280.1704	$280.17	$280.15	$280.20
Purchase #5	$200.71	10.795%	$222.3766	$222.38	$222.40	$222.40
Purchase #6	$41.32	7.612%	$44.4653	$44.47	$44.45	$44.50
Purchase #7	$52.86	7.697%	$56.9286	$56.93	$56.95	$56.90
7 purchase totals =	$1,131.53		$1,247.2619	$1,247.27	$1,247.30	$1,247.30