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 $125.82   8.847%   $136.9513   $136.95   $136.95   $137.00  
  Purchase #2 $200.64   3.655%   $207.9734   $207.97   $207.95   $208.00  
  Purchase #3 $85.55   9.285%   $93.4933   $93.49   $93.50   $93.50  
  Purchase #4 $64.25   4.278%   $66.9986   $67.00   $67.00   $67.00  
  Purchase #5 $113.31   8.247%   $122.6547   $122.65   $122.65   $122.70  
  Purchase #6 $46.92   13.619%   $53.31   $53.31   $53.30   $53.30  
  Purchase #7 $21.84   11.544%   $24.3612   $24.36   $24.35   $24.40  
  7 purchase totals = $658.33       $705.7425   $705.73   $705.70   $705.90