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 $180.49   11.655%   $201.5261   $201.53   $201.55   $201.50  
  Purchase #2 $118.48   4.846%   $124.2215   $124.22   $124.20   $124.20  
  Purchase #3 $43.46   4.126%   $45.2532   $45.25   $45.25   $45.30  
  Purchase #4 $82.92   8.260%   $89.7692   $89.77   $89.75   $89.80  
  Purchase #5 $72.65   5.622%   $76.7344   $76.73   $76.75   $76.70  
  Purchase #6 $221.59   11.510%   $247.095   $247.10   $247.10   $247.10  
  Purchase #7 $215.56   10.629%   $238.4719   $238.47   $238.45   $238.50  
  7 purchase totals = $935.15       $1,023.0713   $1,023.07   $1,023.05   $1,023.10