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 $24.63   8.785%   $26.7937   $26.79   $26.80   $26.80  
  Purchase #2 $127.63   7.229%   $136.8564   $136.86   $136.85   $136.90  
  Purchase #3 $208.43   3.468%   $215.6584   $215.66   $215.65   $215.70  
  Purchase #4 $111.99   13.377%   $126.9709   $126.97   $126.95   $127.00  
  Purchase #5 $241.68   7.663%   $260.1999   $260.20   $260.20   $260.20  
  Purchase #6 $217.77   7.411%   $233.9089   $233.91   $233.90   $233.90  
  Purchase #7 $154.41   13.228%   $174.8354   $174.84   $174.85   $174.80  
  7 purchase totals = $1,086.54       $1,175.2236   $1,175.23   $1,175.20   $1,175.30