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 $66.96   13.825%   $76.2172   $76.22   $76.20   $76.20  
  Purchase #2 $88.45   3.545%   $91.5856   $91.59   $91.60   $91.60  
  Purchase #3 $20.61   8.277%   $22.3159   $22.32   $22.30   $22.30  
  Purchase #4 $206.42   5.293%   $217.3458   $217.35   $217.35   $217.30  
  Purchase #5 $183.46   13.695%   $208.5848   $208.58   $208.60   $208.60  
  Purchase #6 $76.42   13.431%   $86.684   $86.68   $86.70   $86.70  
  Purchase #7 $110.27   12.439%   $123.9865   $123.99   $124.00   $124.00  
  7 purchase totals = $752.59       $826.7198   $826.73   $826.75   $826.70