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 $58.39   13.462%   $66.2505   $66.25   $66.25   $66.30  
  Purchase #2 $192.26   12.710%   $216.6962   $216.70   $216.70   $216.70  
  Purchase #3 $175.93   3.535%   $182.1491   $182.15   $182.15   $182.10  
  Purchase #4 $21.88   8.620%   $23.7661   $23.77   $23.75   $23.80  
  Purchase #5 $89.67   10.384%   $98.9813   $98.98   $99.00   $99.00  
  Purchase #6 $206.86   9.389%   $226.2821   $226.28   $226.30   $226.30  
  Purchase #7 $107.75   8.605%   $117.0219   $117.02   $117.00   $117.00  
  7 purchase totals = $852.74       $931.1472   $931.15   $931.15   $931.20