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 $182.87   12.631%   $205.9683   $205.97   $205.95   $206.00  
  Purchase #2 $65.51   12.610%   $73.7708   $73.77   $73.75   $73.80  
  Purchase #3 $79.75   8.462%   $86.4984   $86.50   $86.50   $86.50  
  Purchase #4 $28.39   12.772%   $32.016   $32.02   $32.00   $32.00  
  Purchase #5 $185.58   4.227%   $193.4245   $193.42   $193.40   $193.40  
  Purchase #6 $230.97   8.349%   $250.2537   $250.25   $250.25   $250.30  
  Purchase #7 $92.92   13.692%   $105.6426   $105.64   $105.65   $105.60  
  7 purchase totals = $865.99       $947.5743   $947.57   $947.50   $947.60