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	$243.62	5.211%	$256.315	$256.32	$256.30	$256.30
Purchase #2	$196.31	3.537%	$203.2535	$203.25	$203.25	$203.30
Purchase #3	$220.61	9.366%	$241.2723	$241.27	$241.25	$241.30
Purchase #4	$154.35	9.587%	$169.1475	$169.15	$169.15	$169.10
Purchase #5	$154.87	6.501%	$164.9381	$164.94	$164.95	$164.90
Purchase #6	$241.86	12.411%	$271.8772	$271.88	$271.90	$271.90
Purchase #7	$160.28	7.612%	$172.4805	$172.48	$172.50	$172.50
7 purchase totals =	$1,371.90		$1,479.2841	$1,479.29	$1,479.30	$1,479.30