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 $214.28   7.665%   $230.7046   $230.70   $230.70   $230.70  
  Purchase #2 $33.74   7.439%   $36.2499   $36.25   $36.25   $36.20  
  Purchase #3 $73.34   5.522%   $77.3898   $77.39   $77.40   $77.40  
  Purchase #4 $248.55   9.744%   $272.7687   $272.77   $272.75   $272.80  
  Purchase #5 $60.60   12.588%   $68.2283   $68.23   $68.25   $68.20  
  Purchase #6 $76.98   8.578%   $83.5833   $83.58   $83.60   $83.60  
  Purchase #7 $67.66   9.181%   $73.8719   $73.87   $73.85   $73.90  
  7 purchase totals = $775.15       $842.7965   $842.79   $842.80   $842.80