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 $218.33   11.120%   $242.6083   $242.61   $242.60   $242.60  
  Purchase #2 $113.88   8.417%   $123.4653   $123.47   $123.45   $123.50  
  Purchase #3 $58.26   9.353%   $63.7091   $63.71   $63.70   $63.70  
  Purchase #4 $199.30   9.579%   $218.3909   $218.39   $218.40   $218.40  
  Purchase #5 $211.77   8.264%   $229.2707   $229.27   $229.25   $229.30  
  Purchase #6 $106.52   3.655%   $110.4133   $110.41   $110.40   $110.40  
  Purchase #7 $27.86   9.673%   $30.5549   $30.55   $30.55   $30.60  
  7 purchase totals = $935.92       $1,018.4125   $1,018.41   $1,018.35   $1,018.50