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 $6.32   9.772%   $6.9376   $6.94   $6.95   $6.90  
  Purchase #2 $228.44   13.157%   $258.4959   $258.50   $258.50   $258.50  
  Purchase #3 $245.95   4.185%   $256.243   $256.24   $256.25   $256.20  
  Purchase #4 $207.95   5.656%   $219.7117   $219.71   $219.70   $219.70  
  Purchase #5 $102.25   4.476%   $106.8267   $106.83   $106.85   $106.80  
  Purchase #6 $122.37   13.172%   $138.4886   $138.49   $138.50   $138.50  
  Purchase #7 $110.26   4.763%   $115.5117   $115.51   $115.50   $115.50  
  7 purchase totals = $1,023.54       $1,102.2152   $1,102.22   $1,102.25   $1,102.10