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 $52.97   13.852%   $60.3074   $60.31   $60.30   $60.30  
  Purchase #2 $74.42   9.860%   $81.7578   $81.76   $81.75   $81.80  
  Purchase #3 $191.61   4.393%   $200.0274   $200.03   $200.05   $200.00  
  Purchase #4 $142.76   13.661%   $162.2624   $162.26   $162.25   $162.30  
  Purchase #5 $174.80   4.347%   $182.3986   $182.40   $182.40   $182.40  
  Purchase #6 $187.81   10.858%   $208.2024   $208.20   $208.20   $208.20  
  Purchase #7 $205.51   12.665%   $231.5378   $231.54   $231.55   $231.50  
  7 purchase totals = $1,029.88       $1,126.4938   $1,126.50   $1,126.50   $1,126.50