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 $214.96   12.431%   $241.6817   $241.68   $241.70   $241.70  
  Purchase #2 $207.33   7.767%   $223.4333   $223.43   $223.45   $223.40  
  Purchase #3 $59.28   10.153%   $65.2987   $65.30   $65.30   $65.30  
  Purchase #4 $5.92   8.514%   $6.424   $6.42   $6.40   $6.40  
  Purchase #5 $190.38   11.189%   $211.6816   $211.68   $211.70   $211.70  
  Purchase #6 $193.87   5.311%   $204.1664   $204.17   $204.15   $204.20  
  Purchase #7 $246.63   6.188%   $261.8915   $261.89   $261.90   $261.90  
  7 purchase totals = $1,118.37       $1,214.5772   $1,214.57   $1,214.60   $1,214.60