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 $246.63   11.623%   $275.2958   $275.30   $275.30   $275.30  
  Purchase #2 $131.30   4.275%   $136.9131   $136.91   $136.90   $136.90  
  Purchase #3 $197.57   8.353%   $214.073   $214.07   $214.05   $214.10  
  Purchase #4 $217.56   13.357%   $246.6195   $246.62   $246.60   $246.60  
  Purchase #5 $236.31   12.803%   $266.5648   $266.56   $266.55   $266.60  
  Purchase #6 $69.89   13.402%   $79.2567   $79.26   $79.25   $79.30  
  Purchase #7 $196.51   13.370%   $222.7834   $222.78   $222.80   $222.80  
  7 purchase totals = $1,295.77       $1,441.5063   $1,441.50   $1,441.45   $1,441.60