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 $55.62   5.874%   $58.8871   $58.89   $58.90   $58.90  
  Purchase #2 $229.92   3.751%   $238.5443   $238.54   $238.55   $238.50  
  Purchase #3 $164.38   9.459%   $179.9287   $179.93   $179.95   $179.90  
  Purchase #4 $30.77   9.432%   $33.6722   $33.67   $33.65   $33.70  
  Purchase #5 $176.78   4.823%   $185.3061   $185.31   $185.30   $185.30  
  Purchase #6 $136.51   3.685%   $141.5404   $141.54   $141.55   $141.50  
  Purchase #7 $190.64   7.303%   $204.5624   $204.56   $204.55   $204.60  
  7 purchase totals = $984.62       $1,042.4412   $1,042.44   $1,042.45   $1,042.40