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	$248.88	9.182%	$271.7322	$271.73	$271.75	$271.70
Purchase #2	$225.41	13.471%	$255.775	$255.78	$255.80	$255.80
Purchase #3	$76.78	4.370%	$80.1353	$80.14	$80.15	$80.10
Purchase #4	$96.55	13.780%	$109.8546	$109.85	$109.85	$109.90
Purchase #5	$177.98	4.409%	$185.8271	$185.83	$185.85	$185.80
Purchase #6	$7.74	8.488%	$8.397	$8.40	$8.40	$8.40
Purchase #7	$112.52	7.841%	$121.3427	$121.34	$121.35	$121.30
7 purchase totals =	$945.86		$1,033.0639	$1,033.07	$1,033.15	$1,033.00