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 $201.77   11.357%   $224.685   $224.69   $224.70   $224.70  
  Purchase #2 $129.89   6.206%   $137.951   $137.95   $137.95   $138.00  
  Purchase #3 $239.54   7.517%   $257.5462   $257.55   $257.55   $257.50  
  Purchase #4 $86.58   9.195%   $94.541   $94.54   $94.55   $94.50  
  Purchase #5 $162.45   13.758%   $184.7999   $184.80   $184.80   $184.80  
  Purchase #6 $227.92   9.667%   $249.953   $249.95   $249.95   $250.00  
  Purchase #7 $14.73   7.211%   $15.7922   $15.79   $15.80   $15.80  
  7 purchase totals = $1,062.88       $1,165.2683   $1,165.27   $1,165.30   $1,165.30