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 $246.95   10.714%   $273.4082   $273.41   $273.40   $273.40  
  Purchase #2 $175.67   7.339%   $188.5624   $188.56   $188.55   $188.60  
  Purchase #3 $64.63   7.785%   $69.6614   $69.66   $69.65   $69.70  
  Purchase #4 $16.63   10.631%   $18.3979   $18.40   $18.40   $18.40  
  Purchase #5 $191.49   3.612%   $198.4066   $198.41   $198.40   $198.40  
  Purchase #6 $17.28   13.664%   $19.6411   $19.64   $19.65   $19.60  
  Purchase #7 $226.76   13.298%   $256.9145   $256.91   $256.90   $256.90  
  7 purchase totals = $939.41       $1,024.9921   $1,024.99   $1,024.95   $1,025.00