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 $241.45   8.473%   $261.9081   $261.91   $261.90   $261.90  
  Purchase #2 $110.73   11.236%   $123.1716   $123.17   $123.15   $123.20  
  Purchase #3 $57.64   10.299%   $63.5763   $63.58   $63.60   $63.60  
  Purchase #4 $83.63   3.739%   $86.7569   $86.76   $86.75   $86.80  
  Purchase #5 $194.86   12.538%   $219.2915   $219.29   $219.30   $219.30  
  Purchase #6 $82.63   8.190%   $89.3974   $89.40   $89.40   $89.40  
  Purchase #7 $95.68   8.329%   $103.6492   $103.65   $103.65   $103.60  
  7 purchase totals = $866.62       $947.7510   $947.76   $947.75   $947.80