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 $114.66   8.708%   $124.6446   $124.64   $124.65   $124.60  
  Purchase #2 $222.46   4.607%   $232.7087   $232.71   $232.70   $232.70  
  Purchase #3 $174.70   13.380%   $198.0749   $198.07   $198.05   $198.10  
  Purchase #4 $54.84   10.560%   $60.6311   $60.63   $60.65   $60.60  
  Purchase #5 $185.26   8.531%   $201.0645   $201.06   $201.05   $201.10  
  Purchase #6 $13.40   9.345%   $14.6522   $14.65   $14.65   $14.70  
  Purchase #7 $210.40   7.581%   $226.3504   $226.35   $226.35   $226.40  
  7 purchase totals = $975.72       $1,058.1264   $1,058.11   $1,058.10   $1,058.20