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 $188.49   10.432%   $208.1533   $208.15   $208.15   $208.20  
  Purchase #2 $243.64   13.587%   $276.7434   $276.74   $276.75   $276.70  
  Purchase #3 $24.77   7.606%   $26.654   $26.65   $26.65   $26.70  
  Purchase #4 $214.93   6.295%   $228.4598   $228.46   $228.45   $228.50  
  Purchase #5 $104.69   10.169%   $115.3359   $115.34   $115.35   $115.30  
  Purchase #6 $114.65   6.398%   $121.9853   $121.99   $122.00   $122.00  
  Purchase #7 $165.45   12.608%   $186.3099   $186.31   $186.30   $186.30  
  7 purchase totals = $1,056.62       $1,163.6416   $1,163.64   $1,163.65   $1,163.70