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 $242.75   9.818%   $266.5832   $266.58   $266.60   $266.60  
  Purchase #2 $5.69   10.632%   $6.295   $6.30   $6.30   $6.30  
  Purchase #3 $200.49   11.417%   $223.3799   $223.38   $223.40   $223.40  
  Purchase #4 $52.76   7.755%   $56.8515   $56.85   $56.85   $56.90  
  Purchase #5 $65.70   10.715%   $72.7398   $72.74   $72.75   $72.70  
  Purchase #6 $217.46   8.326%   $235.5657   $235.57   $235.55   $235.60  
  Purchase #7 $168.88   3.334%   $174.5105   $174.51   $174.50   $174.50  
  7 purchase totals = $953.73       $1,035.9256   $1,035.93   $1,035.95   $1,036.00