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	$97.53	5.812%	$103.1984	$103.20	$103.20	$103.20
Purchase #2	$123.69	12.732%	$139.4382	$139.44	$139.45	$139.40
Purchase #3	$163.34	13.492%	$185.3778	$185.38	$185.40	$185.40
Purchase #4	$89.35	6.617%	$95.2623	$95.26	$95.25	$95.30
Purchase #5	$37.34	9.633%	$40.937	$40.94	$40.95	$40.90
Purchase #6	$169.61	4.289%	$176.8846	$176.88	$176.90	$176.90
Purchase #7	$240.84	10.249%	$265.5237	$265.52	$265.50	$265.50
7 purchase totals =	$921.70		$1,006.6220	$1,006.62	$1,006.65	$1,006.60