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 $249.92   5.558%   $263.8106   $263.81   $263.80   $263.80  
  Purchase #2 $157.53   6.744%   $168.1538   $168.15   $168.15   $168.20  
  Purchase #3 $39.67   12.298%   $44.5486   $44.55   $44.55   $44.50  
  Purchase #4 $117.25   7.459%   $125.9957   $126.00   $126.00   $126.00  
  Purchase #5 $98.35   8.396%   $106.6075   $106.61   $106.60   $106.60  
  Purchase #6 $76.95   9.166%   $84.0032   $84.00   $84.00   $84.00  
  Purchase #7 $117.87   13.161%   $133.3829   $133.38   $133.40   $133.40  
  7 purchase totals = $857.54       $926.5023   $926.50   $926.50   $926.50