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 $58.26   11.848%   $65.1626   $65.16   $65.15   $65.20  
  Purchase #2 $249.91   5.638%   $263.9999   $264.00   $264.00   $264.00  
  Purchase #3 $108.91   8.603%   $118.2795   $118.28   $118.30   $118.30  
  Purchase #4 $75.33   3.806%   $78.1971   $78.20   $78.20   $78.20  
  Purchase #5 $241.38   10.127%   $265.8246   $265.82   $265.80   $265.80  
  Purchase #6 $109.69   4.430%   $114.5493   $114.55   $114.55   $114.50  
  Purchase #7 $28.93   3.410%   $29.9165   $29.92   $29.90   $29.90  
  7 purchase totals = $872.41       $935.9295   $935.93   $935.90   $935.90