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 $54.91   10.863%   $60.8749   $60.87   $60.85   $60.90  
  Purchase #2 $248.88   9.242%   $271.8815   $271.88   $271.90   $271.90  
  Purchase #3 $175.53   10.256%   $193.5324   $193.53   $193.55   $193.50  
  Purchase #4 $94.31   8.122%   $101.9699   $101.97   $101.95   $102.00  
  Purchase #5 $43.25   10.699%   $47.8773   $47.88   $47.90   $47.90  
  Purchase #6 $177.42   11.832%   $198.4123   $198.41   $198.40   $198.40  
  Purchase #7 $127.91   12.115%   $143.4063   $143.41   $143.40   $143.40  
  7 purchase totals = $922.21       $1,017.9546   $1,017.95   $1,017.95   $1,018.00