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 $235.35   12.195%   $264.0509   $264.05   $264.05   $264.10  
  Purchase #2 $152.63   7.612%   $164.2482   $164.25   $164.25   $164.20  
  Purchase #3 $14.40   10.173%   $15.8649   $15.86   $15.85   $15.90  
  Purchase #4 $200.59   13.358%   $227.3848   $227.38   $227.40   $227.40  
  Purchase #5 $147.32   8.303%   $159.552   $159.55   $159.55   $159.60  
  Purchase #6 $51.98   12.255%   $58.3501   $58.35   $58.35   $58.40  
  Purchase #7 $124.87   9.261%   $136.4342   $136.43   $136.45   $136.40  
  7 purchase totals = $927.14       $1,025.8851   $1,025.87   $1,025.90   $1,026.00