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 $233.80   12.577%   $263.205   $263.21   $263.20   $263.20  
  Purchase #2 $86.38   6.131%   $91.676   $91.68   $91.70   $91.70  
  Purchase #3 $142.85   9.527%   $156.4593   $156.46   $156.45   $156.50  
  Purchase #4 $236.32   6.671%   $252.0849   $252.08   $252.10   $252.10  
  Purchase #5 $125.54   7.873%   $135.4238   $135.42   $135.40   $135.40  
  Purchase #6 $24.69   7.498%   $26.5413   $26.54   $26.55   $26.50  
  Purchase #7 $128.39   10.259%   $141.5615   $141.56   $141.55   $141.60  
  7 purchase totals = $977.97       $1,066.9518   $1,066.95   $1,066.95   $1,067.00