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 $136.41   11.788%   $152.49   $152.49   $152.50   $152.50  
  Purchase #2 $138.91   11.559%   $154.9666   $154.97   $154.95   $155.00  
  Purchase #3 $23.49   13.671%   $26.7013   $26.70   $26.70   $26.70  
  Purchase #4 $53.99   6.499%   $57.4988   $57.50   $57.50   $57.50  
  Purchase #5 $95.26   11.541%   $106.254   $106.25   $106.25   $106.30  
  Purchase #6 $118.30   8.229%   $128.0349   $128.03   $128.05   $128.00  
  Purchase #7 $26.32   4.695%   $27.5557   $27.56   $27.55   $27.60  
  7 purchase totals = $592.68       $653.5013   $653.50   $653.50   $653.60