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	$137.83	5.418%	$145.2976	$145.30	$145.30	$145.30
Purchase #2	$97.48	12.768%	$109.9262	$109.93	$109.95	$109.90
Purchase #3	$239.47	9.569%	$262.3849	$262.38	$262.40	$262.40
Purchase #4	$190.79	4.249%	$198.8967	$198.90	$198.90	$198.90
Purchase #5	$221.92	9.856%	$243.7924	$243.79	$243.80	$243.80
Purchase #6	$113.34	8.723%	$123.2266	$123.23	$123.25	$123.20
Purchase #7	$186.37	5.481%	$196.5849	$196.58	$196.60	$196.60
7 purchase totals =	$1,187.20		$1,280.1093	$1,280.11	$1,280.20	$1,280.10