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 $69.35   3.817%   $71.9971   $72.00   $72.00   $72.00  
  Purchase #2 $147.64   10.558%   $163.2278   $163.23   $163.25   $163.20  
  Purchase #3 $61.76   3.549%   $63.9519   $63.95   $63.95   $64.00  
  Purchase #4 $125.97   10.806%   $139.5823   $139.58   $139.60   $139.60  
  Purchase #5 $250.81   4.206%   $261.3591   $261.36   $261.35   $261.40  
  Purchase #6 $49.63   13.268%   $56.2149   $56.21   $56.20   $56.20  
  Purchase #7 $210.51   9.270%   $230.0243   $230.02   $230.00   $230.00  
  7 purchase totals = $915.67       $986.3574   $986.35   $986.35   $986.40