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 $24.58   8.868%   $26.7598   $26.76   $26.75   $26.80  
  Purchase #2 $74.83   8.176%   $80.9481   $80.95   $80.95   $80.90  
  Purchase #3 $171.57   13.564%   $194.8418   $194.84   $194.85   $194.80  
  Purchase #4 $226.49   6.459%   $241.119   $241.12   $241.10   $241.10  
  Purchase #5 $6.74   9.283%   $7.3657   $7.37   $7.35   $7.40  
  Purchase #6 $17.91   6.605%   $19.093   $19.09   $19.10   $19.10  
  Purchase #7 $165.97   13.426%   $188.2531   $188.25   $188.25   $188.30  
  7 purchase totals = $688.09       $758.3805   $758.38   $758.35   $758.40