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 $238.46   11.602%   $266.1261   $266.13   $266.15   $266.10  
  Purchase #2 $235.47   9.234%   $257.2133   $257.21   $257.20   $257.20  
  Purchase #3 $225.66   5.592%   $238.2789   $238.28   $238.30   $238.30  
  Purchase #4 $106.92   10.275%   $117.906   $117.91   $117.90   $117.90  
  Purchase #5 $92.68   3.116%   $95.5679   $95.57   $95.55   $95.60  
  Purchase #6 $70.29   8.694%   $76.401   $76.40   $76.40   $76.40  
  Purchase #7 $63.54   12.436%   $71.4418   $71.44   $71.45   $71.40  
  7 purchase totals = $1,033.02       $1,122.9350   $1,122.94   $1,122.95   $1,122.90