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 $58.31   8.737%   $63.4045   $63.40   $63.40   $63.40  
  Purchase #2 $82.36   11.199%   $91.5835   $91.58   $91.60   $91.60  
  Purchase #3 $170.99   13.217%   $193.5897   $193.59   $193.60   $193.60  
  Purchase #4 $240.65   11.515%   $268.3608   $268.36   $268.35   $268.40  
  Purchase #5 $172.61   13.225%   $195.4377   $195.44   $195.45   $195.40  
  Purchase #6 $35.48   8.839%   $38.6161   $38.62   $38.60   $38.60  
  Purchase #7 $235.63   7.253%   $252.7202   $252.72   $252.70   $252.70  
  7 purchase totals = $996.03       $1,103.7125   $1,103.71   $1,103.70   $1,103.70