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 $107.58   13.787%   $122.4121   $122.41   $122.40   $122.40  
  Purchase #2 $210.87   9.723%   $231.3729   $231.37   $231.35   $231.40  
  Purchase #3 $211.35   8.529%   $229.376   $229.38   $229.40   $229.40  
  Purchase #4 $22.59   9.316%   $24.6945   $24.69   $24.70   $24.70  
  Purchase #5 $196.85   3.215%   $203.1787   $203.18   $203.20   $203.20  
  Purchase #6 $207.81   9.352%   $227.2444   $227.24   $227.25   $227.20  
  Purchase #7 $64.44   7.250%   $69.1119   $69.11   $69.10   $69.10  
  7 purchase totals = $1,021.49       $1,107.3905   $1,107.38   $1,107.40   $1,107.40