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	$226.91	3.384%	$234.5886	$234.59	$234.60	$234.60
Purchase #2	$65.47	9.833%	$71.9077	$71.91	$71.90	$71.90
Purchase #3	$149.67	10.247%	$165.0067	$165.01	$165.00	$165.00
Purchase #4	$111.83	6.547%	$119.1515	$119.15	$119.15	$119.20
Purchase #5	$214.44	7.776%	$231.1149	$231.11	$231.10	$231.10
Purchase #6	$16.44	3.476%	$17.0115	$17.01	$17.00	$17.00
Purchase #7	$154.48	6.190%	$164.0423	$164.04	$164.05	$164.00
7 purchase totals =	$939.24		$1,002.8232	$1,002.82	$1,002.80	$1,002.80