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 $231.53   6.276%   $246.0608   $246.06   $246.05   $246.10  
  Purchase #2 $58.53   3.136%   $60.3655   $60.37   $60.35   $60.40  
  Purchase #3 $146.56   10.363%   $161.748   $161.75   $161.75   $161.70  
  Purchase #4 $176.64   5.126%   $185.6946   $185.69   $185.70   $185.70  
  Purchase #5 $20.81   7.841%   $22.4417   $22.44   $22.45   $22.40  
  Purchase #6 $207.33   8.576%   $225.1106   $225.11   $225.10   $225.10  
  Purchase #7 $110.83   10.577%   $122.5525   $122.55   $122.55   $122.60  
  7 purchase totals = $952.23       $1,023.9737   $1,023.97   $1,023.95   $1,024.00