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 $91.77   13.833%   $104.4645   $104.46   $104.45   $104.50  
  Purchase #2 $208.98   7.866%   $225.4184   $225.42   $225.40   $225.40  
  Purchase #3 $199.49   10.812%   $221.0589   $221.06   $221.05   $221.10  
  Purchase #4 $92.48   11.356%   $102.982   $102.98   $103.00   $103.00  
  Purchase #5 $24.34   12.439%   $27.3677   $27.37   $27.35   $27.40  
  Purchase #6 $241.43   7.176%   $258.755   $258.76   $258.75   $258.80  
  Purchase #7 $86.97   7.696%   $93.6632   $93.66   $93.65   $93.70  
  7 purchase totals = $945.46       $1,033.7097   $1,033.71   $1,033.65   $1,033.90