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 $162.95   7.361%   $174.9447   $174.94   $174.95   $174.90  
  Purchase #2 $93.26   12.483%   $104.9016   $104.90   $104.90   $104.90  
  Purchase #3 $42.87   12.324%   $48.1533   $48.15   $48.15   $48.20  
  Purchase #4 $28.91   6.773%   $30.8681   $30.87   $30.85   $30.90  
  Purchase #5 $163.72   6.226%   $173.9132   $173.91   $173.90   $173.90  
  Purchase #6 $245.65   6.299%   $261.1235   $261.12   $261.10   $261.10  
  Purchase #7 $249.75   9.385%   $273.189   $273.19   $273.20   $273.20  
  7 purchase totals = $987.11       $1,067.0934   $1,067.08   $1,067.05   $1,067.10