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	$148.59	4.127%	$154.7223	$154.72	$154.70	$154.70
Purchase #2	$166.62	9.759%	$182.8804	$182.88	$182.90	$182.90
Purchase #3	$9.91	12.592%	$11.1579	$11.16	$11.15	$11.20
Purchase #4	$218.57	10.264%	$241.004	$241.00	$241.00	$241.00
Purchase #5	$92.52	4.227%	$96.4308	$96.43	$96.45	$96.40
Purchase #6	$68.63	4.471%	$71.6984	$71.70	$71.70	$71.70
Purchase #7	$52.61	13.826%	$59.8839	$59.88	$59.90	$59.90
7 purchase totals =	$757.45		$817.7777	$817.77	$817.80	$817.80