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 $60.44   4.716%   $63.2904   $63.29   $63.30   $63.30  
  Purchase #2 $186.81   6.310%   $198.5977   $198.60   $198.60   $198.60  
  Purchase #3 $245.91   10.842%   $272.5716   $272.57   $272.55   $272.60  
  Purchase #4 $30.38   8.453%   $32.948   $32.95   $32.95   $32.90  
  Purchase #5 $248.69   13.779%   $282.957   $282.96   $282.95   $283.00  
  Purchase #6 $51.51   6.780%   $55.0024   $55.00   $55.00   $55.00  
  Purchase #7 $28.83   6.158%   $30.6054   $30.61   $30.60   $30.60  
  7 purchase totals = $852.57       $935.9725   $935.98   $935.95   $936.00