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 $30.85   7.195%   $33.0697   $33.07   $33.05   $33.10  
  Purchase #2 $205.83   6.254%   $218.7026   $218.70   $218.70   $218.70  
  Purchase #3 $28.96   7.226%   $31.0526   $31.05   $31.05   $31.10  
  Purchase #4 $68.32   11.716%   $76.3244   $76.32   $76.30   $76.30  
  Purchase #5 $72.72   11.801%   $81.3017   $81.30   $81.30   $81.30  
  Purchase #6 $225.96   3.283%   $233.3783   $233.38   $233.40   $233.40  
  Purchase #7 $20.70   13.748%   $23.5458   $23.55   $23.55   $23.50  
  7 purchase totals = $653.34       $697.3751   $697.37   $697.35   $697.40