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 $244.65   7.365%   $262.6685   $262.67   $262.65   $262.70  
  Purchase #2 $155.66   5.538%   $164.2805   $164.28   $164.30   $164.30  
  Purchase #3 $50.92   12.830%   $57.453   $57.45   $57.45   $57.50  
  Purchase #4 $218.48   12.715%   $246.2597   $246.26   $246.25   $246.30  
  Purchase #5 $186.30   8.379%   $201.9101   $201.91   $201.90   $201.90  
  Purchase #6 $44.60   6.412%   $47.4598   $47.46   $47.45   $47.50  
  Purchase #7 $13.55   4.856%   $14.208   $14.21   $14.20   $14.20  
  7 purchase totals = $914.16       $994.2396   $994.24   $994.20   $994.40