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 $242.98   5.864%   $257.2283   $257.23   $257.25   $257.20  
  Purchase #2 $105.64   7.676%   $113.7489   $113.75   $113.75   $113.70  
  Purchase #3 $50.42   6.431%   $53.6625   $53.66   $53.65   $53.70  
  Purchase #4 $164.48   3.176%   $169.7039   $169.70   $169.70   $169.70  
  Purchase #5 $74.74   5.643%   $78.9576   $78.96   $78.95   $79.00  
  Purchase #6 $232.46   8.695%   $252.6724   $252.67   $252.65   $252.70  
  Purchase #7 $82.83   12.334%   $93.0463   $93.05   $93.05   $93.00  
  7 purchase totals = $953.55       $1,019.0199   $1,019.02   $1,019.00   $1,019.00