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 $233.40   13.539%   $265   $265.00   $265.00   $265.00  
  Purchase #2 $220.30   6.533%   $234.6922   $234.69   $234.70   $234.70  
  Purchase #3 $212.76   6.127%   $225.7958   $225.80   $225.80   $225.80  
  Purchase #4 $107.33   6.461%   $114.2646   $114.26   $114.25   $114.30  
  Purchase #5 $119.50   11.816%   $133.6201   $133.62   $133.60   $133.60  
  Purchase #6 $239.36   10.395%   $264.2415   $264.24   $264.25   $264.20  
  Purchase #7 $26.79   8.351%   $29.0272   $29.03   $29.05   $29.00  
  7 purchase totals = $1,159.44       $1,266.6414   $1,266.64   $1,266.65   $1,266.60