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 $24.49   7.139%   $26.2383   $26.24   $26.25   $26.20  
  Purchase #2 $239.85   4.321%   $250.2139   $250.21   $250.20   $250.20  
  Purchase #3 $45.83   8.859%   $49.8901   $49.89   $49.90   $49.90  
  Purchase #4 $86.55   11.765%   $96.7326   $96.73   $96.75   $96.70  
  Purchase #5 $98.86   6.407%   $105.194   $105.19   $105.20   $105.20  
  Purchase #6 $176.67   9.289%   $193.0809   $193.08   $193.10   $193.10  
  Purchase #7 $218.67   7.185%   $234.3814   $234.38   $234.40   $234.40  
  7 purchase totals = $890.92       $955.7312   $955.72   $955.80   $955.70