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	$8.41	13.382%	$9.5354	$9.54	$9.55	$9.50
Purchase #2	$112.89	3.427%	$116.7587	$116.76	$116.75	$116.80
Purchase #3	$76.80	4.337%	$80.1308	$80.13	$80.15	$80.10
Purchase #4	$185.51	9.439%	$203.0203	$203.02	$203.00	$203.00
Purchase #5	$78.70	13.768%	$89.5354	$89.54	$89.55	$89.50
Purchase #6	$191.66	10.291%	$211.3837	$211.38	$211.40	$211.40
Purchase #7	$96.30	13.442%	$109.2446	$109.24	$109.25	$109.20
7 purchase totals =	$750.27		$819.6089	$819.61	$819.65	$819.50