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 $69.32   6.526%   $73.8438   $73.84   $73.85   $73.80  
  Purchase #2 $208.25   13.332%   $236.0139   $236.01   $236.00   $236.00  
  Purchase #3 $115.88   8.756%   $126.0265   $126.03   $126.05   $126.00  
  Purchase #4 $237.55   11.295%   $264.3813   $264.38   $264.40   $264.40  
  Purchase #5 $145.76   10.457%   $161.0021   $161.00   $161.00   $161.00  
  Purchase #6 $228.74   9.172%   $249.72   $249.72   $249.70   $249.70  
  Purchase #7 $106.88   13.641%   $121.4595   $121.46   $121.45   $121.50  
  7 purchase totals = $1,112.38       $1,232.4471   $1,232.44   $1,232.45   $1,232.40