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 $182.91   13.205%   $207.0633   $207.06   $207.05   $207.10  
  Purchase #2 $105.49   8.493%   $114.4493   $114.45   $114.45   $114.40  
  Purchase #3 $250.80   10.673%   $277.5679   $277.57   $277.55   $277.60  
  Purchase #4 $209.56   12.465%   $235.6817   $235.68   $235.70   $235.70  
  Purchase #5 $132.50   10.576%   $146.5132   $146.51   $146.50   $146.50  
  Purchase #6 $49.47   6.254%   $52.5639   $52.56   $52.55   $52.60  
  Purchase #7 $26.94   11.775%   $30.1122   $30.11   $30.10   $30.10  
  7 purchase totals = $957.67       $1,063.9515   $1,063.94   $1,063.90   $1,064.00