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 $21.85   12.509%   $24.5832   $24.58   $24.60   $24.60  
  Purchase #2 $208.59   3.383%   $215.6466   $215.65   $215.65   $215.60  
  Purchase #3 $162.55   7.744%   $175.1379   $175.14   $175.15   $175.10  
  Purchase #4 $223.28   6.424%   $237.6235   $237.62   $237.60   $237.60  
  Purchase #5 $216.74   10.669%   $239.864   $239.86   $239.85   $239.90  
  Purchase #6 $148.90   11.199%   $165.5753   $165.58   $165.60   $165.60  
  Purchase #7 $96.56   11.542%   $107.705   $107.71   $107.70   $107.70  
  7 purchase totals = $1,078.47       $1,166.1355   $1,166.14   $1,166.15   $1,166.10