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 $74.61   4.163%   $77.716   $77.72   $77.70   $77.70  
  Purchase #2 $242.83   8.264%   $262.8975   $262.90   $262.90   $262.90  
  Purchase #3 $122.63   6.556%   $130.6696   $130.67   $130.65   $130.70  
  Purchase #4 $17.47   6.365%   $18.582   $18.58   $18.60   $18.60  
  Purchase #5 $75.56   13.469%   $85.7372   $85.74   $85.75   $85.70  
  Purchase #6 $247.36   4.102%   $257.5067   $257.51   $257.50   $257.50  
  Purchase #7 $175.71   5.855%   $185.9978   $186.00   $186.00   $186.00  
  7 purchase totals = $956.17       $1,019.1068   $1,019.12   $1,019.10   $1,019.10