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 $168.99   8.104%   $182.6849   $182.68   $182.70   $182.70  
  Purchase #2 $227.49   13.872%   $259.0474   $259.05   $259.05   $259.00  
  Purchase #3 $5.56   12.673%   $6.2646   $6.26   $6.25   $6.30  
  Purchase #4 $30.86   12.585%   $34.7437   $34.74   $34.75   $34.70  
  Purchase #5 $57.35   10.787%   $63.5363   $63.54   $63.55   $63.50  
  Purchase #6 $22.92   6.688%   $24.4529   $24.45   $24.45   $24.50  
  Purchase #7 $160.87   9.141%   $175.5751   $175.58   $175.60   $175.60  
  7 purchase totals = $674.04       $746.3049   $746.30   $746.35   $746.30