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 $236.56   7.654%   $254.6663   $254.67   $254.65   $254.70  
  Purchase #2 $152.98   12.247%   $171.7155   $171.72   $171.70   $171.70  
  Purchase #3 $110.76   11.723%   $123.7444   $123.74   $123.75   $123.70  
  Purchase #4 $54.97   11.420%   $61.2476   $61.25   $61.25   $61.20  
  Purchase #5 $86.79   10.181%   $95.6261   $95.63   $95.65   $95.60  
  Purchase #6 $27.77   9.381%   $30.3751   $30.38   $30.40   $30.40  
  Purchase #7 $113.34   8.542%   $123.0215   $123.02   $123.00   $123.00  
  7 purchase totals = $783.17       $860.3965   $860.41   $860.40   $860.30