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 $90.89   3.253%   $93.8467   $93.85   $93.85   $93.80  
  Purchase #2 $225.30   11.379%   $250.9369   $250.94   $250.95   $250.90  
  Purchase #3 $107.26   9.244%   $117.1751   $117.18   $117.20   $117.20  
  Purchase #4 $68.34   13.611%   $77.6418   $77.64   $77.65   $77.60  
  Purchase #5 $106.45   6.806%   $113.695   $113.70   $113.70   $113.70  
  Purchase #6 $154.27   7.284%   $165.507   $165.51   $165.50   $165.50  
  Purchase #7 $186.72   11.293%   $207.8063   $207.81   $207.80   $207.80  
  7 purchase totals = $939.23       $1,026.6088   $1,026.63   $1,026.65   $1,026.50