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 $32.39   9.307%   $35.4045   $35.40   $35.40   $35.40  
  Purchase #2 $195.89   4.756%   $205.2065   $205.21   $205.20   $205.20  
  Purchase #3 $192.47   12.671%   $216.8579   $216.86   $216.85   $216.90  
  Purchase #4 $81.93   3.868%   $85.0991   $85.10   $85.10   $85.10  
  Purchase #5 $192.42   4.782%   $201.6215   $201.62   $201.60   $201.60  
  Purchase #6 $198.44   4.829%   $208.0227   $208.02   $208.00   $208.00  
  Purchase #7 $60.38   10.207%   $66.543   $66.54   $66.55   $66.50  
  7 purchase totals = $953.92       $1,018.7552   $1,018.75   $1,018.70   $1,018.70