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 $11.33   11.257%   $12.6054   $12.61   $12.60   $12.60  
  Purchase #2 $68.66   6.520%   $73.1366   $73.14   $73.15   $73.10  
  Purchase #3 $192.61   8.496%   $208.9741   $208.97   $208.95   $209.00  
  Purchase #4 $63.68   7.825%   $68.663   $68.66   $68.65   $68.70  
  Purchase #5 $181.25   13.621%   $205.9381   $205.94   $205.95   $205.90  
  Purchase #6 $161.62   10.581%   $178.721   $178.72   $178.70   $178.70  
  Purchase #7 $35.70   7.159%   $38.2558   $38.26   $38.25   $38.30  
  7 purchase totals = $714.85       $786.2940   $786.30   $786.25   $786.30