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 $233.58   4.423%   $243.9112   $243.91   $243.90   $243.90  
  Purchase #2 $40.56   10.645%   $44.8776   $44.88   $44.90   $44.90  
  Purchase #3 $190.64   5.676%   $201.4607   $201.46   $201.45   $201.50  
  Purchase #4 $114.54   4.714%   $119.9394   $119.94   $119.95   $119.90  
  Purchase #5 $43.94   7.179%   $47.0945   $47.09   $47.10   $47.10  
  Purchase #6 $123.71   12.827%   $139.5783   $139.58   $139.60   $139.60  
  Purchase #7 $201.68   7.736%   $217.282   $217.28   $217.30   $217.30  
  7 purchase totals = $948.65       $1,014.1437   $1,014.14   $1,014.20   $1,014.20