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 $247.71   6.276%   $263.2563   $263.26   $263.25   $263.30  
  Purchase #2 $10.40   12.551%   $11.7053   $11.71   $11.70   $11.70  
  Purchase #3 $149.99   10.510%   $165.7539   $165.75   $165.75   $165.80  
  Purchase #4 $122.31   6.448%   $130.1965   $130.20   $130.20   $130.20  
  Purchase #5 $102.86   4.771%   $107.7675   $107.77   $107.75   $107.80  
  Purchase #6 $79.32   4.177%   $82.6332   $82.63   $82.65   $82.60  
  Purchase #7 $241.82   8.607%   $262.6334   $262.63   $262.65   $262.60  
  7 purchase totals = $954.41       $1,023.9461   $1,023.95   $1,023.95   $1,024.00