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 $60.83   10.145%   $67.0012   $67.00   $67.00   $67.00  
  Purchase #2 $32.64   12.466%   $36.7089   $36.71   $36.70   $36.70  
  Purchase #3 $207.32   7.103%   $222.0459   $222.05   $222.05   $222.00  
  Purchase #4 $84.44   10.299%   $93.1365   $93.14   $93.15   $93.10  
  Purchase #5 $216.97   5.721%   $229.3829   $229.38   $229.40   $229.40  
  Purchase #6 $63.85   5.819%   $67.5654   $67.57   $67.55   $67.60  
  Purchase #7 $156.54   9.636%   $171.6242   $171.62   $171.60   $171.60  
  7 purchase totals = $822.59       $887.4650   $887.47   $887.45   $887.40