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 $179.83   8.664%   $195.4105   $195.41   $195.40   $195.40  
  Purchase #2 $114.55   10.555%   $126.6408   $126.64   $126.65   $126.60  
  Purchase #3 $177.91   8.839%   $193.6355   $193.64   $193.65   $193.60  
  Purchase #4 $60.99   3.723%   $63.2607   $63.26   $63.25   $63.30  
  Purchase #5 $147.41   6.631%   $157.1848   $157.18   $157.20   $157.20  
  Purchase #6 $232.56   3.769%   $241.3252   $241.33   $241.35   $241.30  
  Purchase #7 $28.96   11.179%   $32.1974   $32.20   $32.20   $32.20  
  7 purchase totals = $942.21       $1,009.6549   $1,009.66   $1,009.70   $1,009.60