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 $32.71   6.576%   $34.861   $34.86   $34.85   $34.90  
  Purchase #2 $146.99   5.717%   $155.3934   $155.39   $155.40   $155.40  
  Purchase #3 $108.66   5.387%   $114.5135   $114.51   $114.50   $114.50  
  Purchase #4 $169.74   7.741%   $182.8796   $182.88   $182.90   $182.90  
  Purchase #5 $78.97   4.699%   $82.6808   $82.68   $82.70   $82.70  
  Purchase #6 $207.86   6.786%   $221.9654   $221.97   $221.95   $222.00  
  Purchase #7 $204.74   3.316%   $211.5292   $211.53   $211.55   $211.50  
  7 purchase totals = $949.67       $1,003.8229   $1,003.82   $1,003.85   $1,003.90