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	$35.33	10.714%	$39.1153	$39.12	$39.10	$39.10
Purchase #2	$59.61	10.235%	$65.7111	$65.71	$65.70	$65.70
Purchase #3	$166.93	12.517%	$187.8246	$187.82	$187.80	$187.80
Purchase #4	$202.42	10.838%	$224.3583	$224.36	$224.35	$224.40
Purchase #5	$215.32	3.395%	$222.6301	$222.63	$222.65	$222.60
Purchase #6	$171.31	7.166%	$183.5861	$183.59	$183.60	$183.60
Purchase #7	$168.34	4.688%	$176.2318	$176.23	$176.25	$176.20
7 purchase totals =	$1,019.26		$1,099.4573	$1,099.46	$1,099.45	$1,099.40