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 $227.56   8.134%   $246.0697   $246.07   $246.05   $246.10  
  Purchase #2 $218.48   6.193%   $232.0105   $232.01   $232.00   $232.00  
  Purchase #3 $111.46   6.647%   $118.8687   $118.87   $118.85   $118.90  
  Purchase #4 $23.71   4.331%   $24.7369   $24.74   $24.75   $24.70  
  Purchase #5 $52.39   10.706%   $57.9989   $58.00   $58.00   $58.00  
  Purchase #6 $119.95   6.198%   $127.3845   $127.38   $127.40   $127.40  
  Purchase #7 $233.69   10.740%   $258.7883   $258.79   $258.80   $258.80  
  7 purchase totals = $987.24       $1,065.8575   $1,065.86   $1,065.85   $1,065.90