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 $242.73   12.708%   $273.5761   $273.58   $273.60   $273.60  
  Purchase #2 $81.32   12.701%   $91.6485   $91.65   $91.65   $91.60  
  Purchase #3 $227.85   7.733%   $245.4696   $245.47   $245.45   $245.50  
  Purchase #4 $33.31   10.213%   $36.712   $36.71   $36.70   $36.70  
  Purchase #5 $79.84   8.108%   $86.3134   $86.31   $86.30   $86.30  
  Purchase #6 $225.81   8.693%   $245.4397   $245.44   $245.45   $245.40  
  Purchase #7 $30.77   13.338%   $34.8741   $34.87   $34.85   $34.90  
  7 purchase totals = $921.63       $1,014.0334   $1,014.03   $1,014.00   $1,014.00