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 $68.92   10.812%   $76.3716   $76.37   $76.35   $76.40  
  Purchase #2 $196.33   11.403%   $218.7175   $218.72   $218.70   $218.70  
  Purchase #3 $107.80   6.635%   $114.9525   $114.95   $114.95   $115.00  
  Purchase #4 $156.36   4.405%   $163.2477   $163.25   $163.25   $163.20  
  Purchase #5 $90.25   10.400%   $99.636   $99.64   $99.65   $99.60  
  Purchase #6 $176.94   12.294%   $198.693   $198.69   $198.70   $198.70  
  Purchase #7 $207.88   11.723%   $232.2498   $232.25   $232.25   $232.20  
  7 purchase totals = $1,004.48       $1,103.8681   $1,103.87   $1,103.85   $1,103.80