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 $150.31   10.446%   $166.0114   $166.01   $166.00   $166.00  
  Purchase #2 $51.41   9.634%   $56.3628   $56.36   $56.35   $56.40  
  Purchase #3 $47.70   9.416%   $52.1914   $52.19   $52.20   $52.20  
  Purchase #4 $114.72   8.634%   $124.6249   $124.62   $124.60   $124.60  
  Purchase #5 $237.83   8.320%   $257.6175   $257.62   $257.60   $257.60  
  Purchase #6 $235.71   12.656%   $265.5415   $265.54   $265.55   $265.50  
  Purchase #7 $87.57   3.572%   $90.698   $90.70   $90.70   $90.70  
  7 purchase totals = $925.25       $1,013.0475   $1,013.04   $1,013.00   $1,013.00