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 $69.38   10.841%   $76.9015   $76.90   $76.90   $76.90  
  Purchase #2 $155.43   12.695%   $175.1618   $175.16   $175.15   $175.20  
  Purchase #3 $72.38   13.134%   $81.8864   $81.89   $81.90   $81.90  
  Purchase #4 $207.42   4.393%   $216.532   $216.53   $216.55   $216.50  
  Purchase #5 $101.36   8.324%   $109.7972   $109.80   $109.80   $109.80  
  Purchase #6 $8.69   8.280%   $9.4095   $9.41   $9.40   $9.40  
  Purchase #7 $73.54   8.689%   $79.9299   $79.93   $79.95   $79.90  
  7 purchase totals = $688.20       $749.6183   $749.62   $749.65   $749.60