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	$41.91	7.152%	$44.9074	$44.91	$44.90	$44.90
Purchase #2	$207.96	11.837%	$232.5762	$232.58	$232.60	$232.60
Purchase #3	$213.69	8.117%	$231.0352	$231.04	$231.05	$231.00
Purchase #4	$239.97	6.594%	$255.7936	$255.79	$255.80	$255.80
Purchase #5	$112.88	9.108%	$123.1611	$123.16	$123.15	$123.20
Purchase #6	$115.69	10.724%	$128.0966	$128.10	$128.10	$128.10
Purchase #7	$127.31	10.653%	$140.8723	$140.87	$140.85	$140.90
7 purchase totals =	$1,059.41		$1,156.4424	$1,156.45	$1,156.45	$1,156.50