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 $62.82   6.696%   $67.0264   $67.03   $67.05   $67.00  
  Purchase #2 $210.81   8.602%   $228.9439   $228.94   $228.95   $228.90  
  Purchase #3 $143.31   13.338%   $162.4247   $162.42   $162.40   $162.40  
  Purchase #4 $65.34   13.617%   $74.2373   $74.24   $74.25   $74.20  
  Purchase #5 $63.92   8.743%   $69.5085   $69.51   $69.50   $69.50  
  Purchase #6 $183.93   5.788%   $194.5759   $194.58   $194.60   $194.60  
  Purchase #7 $82.55   11.630%   $92.1506   $92.15   $92.15   $92.20  
  7 purchase totals = $812.68       $888.8673   $888.87   $888.90   $888.80