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 $105.27   12.724%   $118.6646   $118.66   $118.65   $118.70  
  Purchase #2 $170.87   11.626%   $190.7353   $190.74   $190.75   $190.70  
  Purchase #3 $201.76   8.186%   $218.2761   $218.28   $218.30   $218.30  
  Purchase #4 $187.62   13.873%   $213.6485   $213.65   $213.65   $213.60  
  Purchase #5 $83.55   13.725%   $95.0172   $95.02   $95.00   $95.00  
  Purchase #6 $54.95   3.383%   $56.809   $56.81   $56.80   $56.80  
  Purchase #7 $171.79   8.435%   $186.2805   $186.28   $186.30   $186.30  
  7 purchase totals = $975.81       $1,079.4312   $1,079.44   $1,079.45   $1,079.40