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 $207.26   13.644%   $235.5386   $235.54   $235.55   $235.50  
  Purchase #2 $104.45   10.246%   $115.1519   $115.15   $115.15   $115.20  
  Purchase #3 $216.79   8.857%   $235.9911   $235.99   $236.00   $236.00  
  Purchase #4 $26.43   13.782%   $30.0726   $30.07   $30.05   $30.10  
  Purchase #5 $240.66   9.157%   $262.6972   $262.70   $262.70   $262.70  
  Purchase #6 $148.45   5.356%   $156.401   $156.40   $156.40   $156.40  
  Purchase #7 $245.77   9.829%   $269.9267   $269.93   $269.95   $269.90  
  7 purchase totals = $1,189.81       $1,305.7791   $1,305.78   $1,305.80   $1,305.80