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	$166.66	10.693%	$184.481	$184.48	$184.50	$184.50
Purchase #2	$121.74	8.800%	$132.4531	$132.45	$132.45	$132.50
Purchase #3	$23.61	7.122%	$25.2915	$25.29	$25.30	$25.30
Purchase #4	$194.77	9.677%	$213.6179	$213.62	$213.60	$213.60
Purchase #5	$80.31	6.137%	$85.2386	$85.24	$85.25	$85.20
Purchase #6	$74.88	5.135%	$78.7251	$78.73	$78.75	$78.70
Purchase #7	$210.93	5.534%	$222.6029	$222.60	$222.60	$222.60
7 purchase totals =	$872.90		$942.4101	$942.41	$942.45	$942.40