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 $186.60   11.165%   $207.4339   $207.43   $207.45   $207.40  
  Purchase #2 $144.66   3.301%   $149.4352   $149.44   $149.45   $149.40  
  Purchase #3 $27.92   9.741%   $30.6397   $30.64   $30.65   $30.60  
  Purchase #4 $84.32   12.580%   $94.9275   $94.93   $94.95   $94.90  
  Purchase #5 $198.94   4.691%   $208.2723   $208.27   $208.25   $208.30  
  Purchase #6 $21.45   4.488%   $22.4127   $22.41   $22.40   $22.40  
  Purchase #7 $50.70   6.571%   $54.0315   $54.03   $54.05   $54.00  
  7 purchase totals = $714.59       $767.1528   $767.15   $767.20   $767.00