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 $122.86   9.136%   $134.0845   $134.08   $134.10   $134.10  
  Purchase #2 $128.69   10.275%   $141.9129   $141.91   $141.90   $141.90  
  Purchase #3 $232.66   12.735%   $262.2893   $262.29   $262.30   $262.30  
  Purchase #4 $221.35   11.411%   $246.6082   $246.61   $246.60   $246.60  
  Purchase #5 $98.87   10.323%   $109.0764   $109.08   $109.10   $109.10  
  Purchase #6 $236.47   8.730%   $257.1138   $257.11   $257.10   $257.10  
  Purchase #7 $173.99   11.208%   $193.4908   $193.49   $193.50   $193.50  
  7 purchase totals = $1,214.89       $1,344.5759   $1,344.57   $1,344.60   $1,344.60