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 $23.46   13.840%   $26.7069   $26.71   $26.70   $26.70  
  Purchase #2 $100.82   12.612%   $113.5354   $113.54   $113.55   $113.50  
  Purchase #3 $193.88   11.233%   $215.6585   $215.66   $215.65   $215.70  
  Purchase #4 $75.33   10.728%   $83.4114   $83.41   $83.40   $83.40  
  Purchase #5 $232.31   6.582%   $247.6006   $247.60   $247.60   $247.60  
  Purchase #6 $121.91   12.419%   $137.05   $137.05   $137.05   $137.10  
  Purchase #7 $206.71   6.621%   $220.3963   $220.40   $220.40   $220.40  
  7 purchase totals = $954.42       $1,044.3591   $1,044.37   $1,044.35   $1,044.40