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 $187.69   7.470%   $201.7104   $201.71   $201.70   $201.70  
  Purchase #2 $59.67   13.400%   $67.6658   $67.67   $67.65   $67.70  
  Purchase #3 $180.83   11.459%   $201.5513   $201.55   $201.55   $201.60  
  Purchase #4 $70.57   8.809%   $76.7865   $76.79   $76.80   $76.80  
  Purchase #5 $137.92   10.189%   $151.9727   $151.97   $151.95   $152.00  
  Purchase #6 $126.44   5.687%   $133.6306   $133.63   $133.65   $133.60  
  Purchase #7 $186.42   10.815%   $206.5813   $206.58   $206.60   $206.60  
  7 purchase totals = $949.54       $1,039.8986   $1,039.90   $1,039.90   $1,040.00