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	$81.43	9.426%	$89.1056	$89.11	$89.10	$89.10
Purchase #2	$39.73	10.833%	$44.034	$44.03	$44.05	$44.00
Purchase #3	$185.45	3.535%	$192.0057	$192.01	$192.00	$192.00
Purchase #4	$104.90	12.227%	$117.7261	$117.73	$117.75	$117.70
Purchase #5	$136.29	4.443%	$142.3454	$142.35	$142.35	$142.30
Purchase #6	$93.42	7.692%	$100.6059	$100.61	$100.60	$100.60
Purchase #7	$71.35	6.658%	$76.1005	$76.10	$76.10	$76.10
7 purchase totals =	$712.57		$761.9232	$761.94	$761.95	$761.80